The US dollar (US$) is used throughout the islands.
Banks with ATMs hooked into worldwide networks (Plus, Cirrus, Exchange etc) are in the main towns on Tortola and Virgin Gorda. Jost Van Dyke, Anegada and the out islands do not have ATMs, so you’ll need to cash up beforehand.
In restaurants, a 15% to 20% tip is the norm; 10% to 15% in taxis. Tip bellhops US$1 to US$2 per bag. A tip of 10% to 20% is reasonable for dive-boat operators and yacht crews.