Indonesia's currency is the Rupiah IDR, abbreviated Rp. The Rupiah's value plummeted during the 1997 economic crisis, but has strengthened again significantly in recent years. The trailing three zeros are often abbreviated with rb ribu, thousand or even dropped completely, and for more expensive items you will often even see jt juta, million.
The largest banknote is the red Rp 100,000, which may only be US$10 but is still inconveniently large for most purchases. Next in the series are Rp 50,000 blue, Rp 20,000 green, Rp 10,000 purple, Rp 5,000 brown, Rp 2,000 gray and finally Rp 1,000. The Rp 1,000 note is discontinued and currently being replaced with a coin. While the new, colorful large-denomination bills are easy to tell apart, the smaller bills and pre-2004 large notes are all confusingly similar pale pastel shades of yellow, green and brown and often filthy and mangled to boot. A chronic shortage of small change — it's not unusual to get a few pieces of candy back instead of coins — has been to some extent alleviated by a new flood of new coins, available in denominations of Rp 1,000, Rp 500. The Rp 200, Rp 100, Rp 50 and the thoroughly useless Rp 25 are being withdrawn during 2012. Older golden metallic versions are also still floating around. Bills printed in 1992 or earlier are no longer in circulation, but can be exchanged at banks. Currently the smaller coins are being withdrawn from circulation.
US dollars are the second currency of Indonesia and will be accepted by anyone in a pinch, but are typically used as an investment and for larger purchases, not buying a bowl of noodles on the street. Many hotels quote rates in dollars, but all accept payment in Rupiah and some who quote in USD then seek to convert the billing into Rupiah for payment. Many will likely use a somewhat disadvantageous rate to do this. If you pay any bill in Indonesia with a credit card it will be charged to your account in Rupiah, regardless of the currency you were quoted. Aside from the US dollar, other major international currencies are also widely accepted for a cash settlement, especially in more touristy areas.
While most commercial places close on Sunday in the West, it does not apply in Indonesia, being a mainly Muslim country. Most of them even have the largest visitors in Sunday and national holidays and shopping malls often become VERY crowded on Sunday. So if you plan to go to Indonesian malls and shopping centres, weekdays Monday to Friday is the best time to visit.
Saturdays and Sundays as well as national holidays are favorite days for Indonesians to go shopping and sightseeing, and as a result, most commercial points open 7 days a week. The notably exceptions are Idul-Fitri Lebaran, end of Ramadan celebration, which most commercials close or open late up to two or three days afterwards though most likely less applied in non-Muslim majority areas like North Sulawesi and Bali, and Indonesian independence day, the 17th of August. To the lesser extent, the same goes with Christmas, particularly in Christian-majority population areas North Sulawesi and parts of North Sumatera and in Chinese-run majority commercials like Glodok or Mangga Dua in Jakarta, as a large number of Indonesian Chinese living in major cities are Christian.
Shopping malls and commercials open at around 10 am, and street shops and traditional markets open as early as 6 am, and close at around 8 to 9 pm. Twenty-four hours stores not malls is not uncommon in major cities.
Living in Indonesia is cheap, as long as you're willing to live like an Indonesian. For example, Rp 10,000 about $1.15 will get you a meal on the street or a packet of cigarettes or three kilometers in a taxi or two bottles of water. But as a tourist it is often necessary to haggle and negotiate a minimum of 50%-70% off an initial asking price, otherwise you will spend your money quickly.
Fancy restaurants, hotels and the like will charge 10% government sales tax plus a variable service charge. This may be denoted with "++" after the price or just written in tiny print on the bottom of the menu.