If entering the country from either Honduras or Costa Rica by land, get rid of those currencies as they are hard to exchange away from the border.
The national currency is called the cordoba NIO. As of February 2015 the official exchange rate is about 26 cordobas to one US dollar. The government deflates the currency about 5% every year to be competitive with the dollar. Most places accept dollars but you will often get change in cordobas and businesses will give you a lower exchange rate. Make sure you have some cordobas handy when using collective buses, taxis, or other small purchases. Nearly all banks exchange US dollars to cordobas but lines are often long, and you may have to use your credit card to get money rather than your bank card. Make sure you bring your passport when exchanging money. All ATMs give cordobas and some can dispense dollars too. Make sure that the ATM you're using is part of the networks listed on the back of your bank card. Though you may be able to find some ATMs that work on the Mastercard/Cirrus system, most will use only the Visa/Plus system.
If you need cordobas when the banks are closed or you can't use your ATM, street licensed money changers or cambistas can be found. Always count your money, though mistakes are rare if you use members of the cambista cooperative. The rate of exchange can be better or worse than at the bank. However, it is rare during normal hours M-F 09:00-17:00 and Saturday to noon to get a worse rate than the banks, though near the markets you might do as bad. Latest example January 2010 - Bank pays NIO21.90 per US dollar, cambistas offer NIO22.10 In Managua, money changers can be found near Pizza Valentis in Los Robles, beside the Dominos Pizza near the BAC Building, and in the Artesania area of Mercado Huembes among other places.
Most modern stores, especially Texaco Star Mart, Esso On The Run, La Union supermarket owned by Wal-Mart will take US currency, often at a slightly better exchange rate than banks or "cambistas" on the streets make sure to look for cambistas' ID badges, with change in cordobas NIO. Limit the bills to USD20 for best success. Cambistas have no problem with USD50 and USD100 bills. They won't accept Euros, Canadian money, or Traveller's Cheques checks. To make sure you have Cordobas for taxis and buses from Augusto Sandino Airport in Managua, you can change US currency for Cordobas at a window right in the airport.
If you are going to take one thing home from Nicaragua it should be a hammock. Nicaraguan hammocks are among the best made and most comfortable ever. The really good ones are made in Masaya, ask a taxi to take you to the fabrica de hamacas, the mercado viejo or the mercado nuevo. You will find the most variety and best prices in Masaya. A simple one person hammock should cost under USD20. Hammocks are also sold in the Huembes market in Managua, which has the only large local goods and arts and crafts section in Managua.
Nicaragua also produces excellent, highly awarded rum called Flor de Caña. This is the most common liquor drunk in Nicaragua. Those aged 4 go for Extra Light over Extra Dry or Etiqueta Negra and particularly 7 years Gran Reserva are a great buy for the money - about USD4-6/bottle. Buy in the local stores as the prices at the duty-free airport shops are higher. Gran Reserva is the best value based on price and quality.
A trip to the artisinal towns of the "Pueblos Blancos" is the most rewarding way to shop for local arts and crafts. The best and easiest location for tourists to buy artisanal items is in the craft market in Masaya. There is a similar market with the same products (from a lot of the same vendors in Mercado Huembes in Managua with slightly lower prices than in the market in Masaya, but vendors and solicitors at Huembes tend to be pushier, especially if they see you`re a "gringo.") Located just 10 minutes from Masaya, 30 minutes from Granada and 40 minutes from Managua, these towns are the arts and crafts centre of Nicaragua. Catarina is home to dozens of nurseries with plants as diverse as this lush tropical country can produce, and also boasts a beautiful view over the Laguna de Apoyo volcanic crater lake where you can enjoy the view from numerous restaurants. San Juan del Oriente is the center of pottery production. You can find dozens of mom and pop studios and stores, meet the artisans and choose from a dazzling and creative array of vases, bowls and other ceramic items. Some of the best shops with more original designs are a few blocks into town off the main highway. Finally, Masatepe is known for its furniture--particularly wicker and wood, and with a special focus on rocking chairs, the favourite Nicaraguan chair. Although you might not be able take any rocking chairs or ferns home with you on the plane, it definitely worth "window" shopping in these picturesque towns. You can also find San Juan del Oriente pottery, Masatepe furniture and other arts and crafts in Masaya, Mercado Huembes in Managua, and in the streets of Granada, Leon and other places visited by tourists. Remember to bargain. Although you may be a tourist, you can still bargain.
Shopping to Western standards is found mainly in Managua in shopping centers, the largest and most modern being MetroCentro near the rotonda Ruben Dario. There are smaller and inferior malls at Plaza Inter and in Bello Horizonte at Plaza Las Americas. A new and large shopping center called Plaza Santo Domingo is located at Carretera Masaya at about Km. 6.
Shopping like the locals takes place at the mercados, or public markets. The largest and must be one of the largest in the Americas is Mercado Oriental. This market contains everything in individual stores or stalls from food to clothes to home electronics. Mercado Oriental is one of the most dangerous locations for tourists in the city. If you go, take only the cash you want to spend. No wallets, watches or jewelry and if you take a cell phone, take it in your pocket not visible to others. It is best to go with a local or better yet a group of locals.
Less frightening, safer and with a similar selection is Mercado Huembes. It is smaller and more open less difficult to get trapped in a dark isolated passage. This market has the aforementioned Masaya artisanal crafts at higher than Masaya prices. There are a few other markets similar in nature, smaller in size, farther away from the beaten track and not worth looking for due to lack of safety and less goods at higher prices.