Beginning March 1, 2015, MasterCard officially began handling credit card transactions by its American cardholders in Cuba, the first US credit card company to do so. However, the range of establishmnets accepting credit cards is limited, and many travelers have reported difficulty using U.S. Mastercards.
Cuba has two currencies: Pesos Cubanos, or National Currency (CUP), and the Cuban Convertible Peso (CUC).
Tipping is always a nice way to show your appreciation for good service. You can tip in both CUP and CUC.
Accommodations and restaurant rates vary considerably, as anywhere. Here is a detailed break-down of travel budget to Cuba.