The currency of Macau is the pataca MOP, which is divided into 100 avos. Prices are shown as $10, for example 10 patacas.
The pataca is pegged to the Hong Kong Dollar HKD at 1.03 patacas to 1 dollar. Hong Kong dollars are accepted by most businesses on a 1:1 basis, but most businesses will endeavour to give you change in HKD if you pay in HKD, if they have them. Occasionally, however, a business might give change in MOP notes and HKD coins or the other way around. The HK$10 coin may not be accepted because of numerous recent forgeries. Chinese renminbi RMB, less often CNY are also accepted in some areas and can easily be changed for either patacas or HKD. In casinos, the HKD is the preferred currency, and gamers with patacas may actually be required to exchange to HKD or HKD-denominated casino chips before playing. Transactions made at government offices though will require you to pay in patacas.
Getting money is quite easy as there are banks and ATMs on nearly every street. Holders of a debit card on the international networks will have no issues withdrawing money. Holders of Chinese Union Pay cards will not have trouble either withdrawing local currency from their accounts. ATMs usually dispense in MOP 100 and 500 bills and HKD 100 and 500 as well and some will also dispense in Chinese currency.
Changing your currency into patacas outside of Macau is just about impossible and pointless. Change enough HKD to tide you over, and then change the rest into patacas after arriving. The money changers at the Barrier Gate provide good exchange rates, and you can also change the HKD you are holding into patacas.
On the other hand, try not to leave Macau with a lot of patacas. Unlike the HKD, they are quite hard to exchange in most countries. Even if you try to exchange them in Hong Kong, money changers may charge high commission thus giving you fewer HKDs than for what the MOP is worth. Therefore because of the 1:1 acceptance between the HKD and MOP and the difficulty exchanging between the two currencies outside Macau, you are advised to use HKD as much as possible for commercial transactions.
Visa and MasterCard credit cards are widely accepted in major restaurants, stores and the ferry terminal but some merchants may require a token minimum purchase amount, usually $100.
Tipping is generally not practised, though bellhops may expect about $10 or so for carrying your bags. In full service restaurants, a service charge is usually imposed and that is taken to be the tip. However, you should know that the 10% service charge does not go to the actual people who served you, rather it is used by the owners to pay the salaries of said employees. If you wish to give a tip, you should give it in cash directly to the person you wish to reward for their good service. Taxi drivers also do not expect tips, and would return exact change, or round it in your favour if they can't be bothered to dig for change.
shopping
Quite frankly, the shopping options in Macau don't hold a candle to Hong Kong. While the newer megacasinos have introduced Macau to the joys of sterile franchise-filled malls, the city center streets around the older casinos are still a bizarre monoculture of ridiculously expensive watch, jewelry and Chinese medicine shops with an emphasis on herbal Viagra-type cures, all aimed squarely at liberating lucky gamblers from their winnings. Finding tasteful souvenirs can thus be surprisingly challenging, although the touristy streets between Largo do Senado and the ruins of St. Paul's do have a scattering of antique shops.
Bargaining in the small shops can be done, but usually working on the principle of the shopkeeper quoting a price, the buyer making "hmmm" sounds and the shopkeeper lowering the price a bit. A full-fledged haggling match is quite rare, as most antique shops sell precisely the same thing at precisely the same prices.