Cuba is primarily a cash economy. Credit cards are accepted in resorts and city hotels. ATMs are widely available and accept some debit/credit cards.
Tipping in Cuba is important. Since most Cubans earn money in moneda nacional (MN$), leaving a tip of CUC$1 or more makes a huge difference.
Resorts/Hotels Tip for good staff service.
Musicians Tip small notes for restaurant musicians when the basket comes around.
Tour guides Depending on tour length (a dollar for a few hours to more for extensive guiding).
Restaurants Standard 10% (up to 15% for excellent service).
Taxis 10% if you're on the meter, otherwise agree full fare beforehand.