Bigger cities have ATMs, but they often run out of money or stop working. Credit cards are usually accepted in the capital but rarely elsewhere.
Most Haitians don't tip, but in tourist areas it is usual to tip and certainly all gratuities are happily accepted. Restaurant bills generally include a 10% tax and a 5% service charge, and if you'd like to add a little extra for great service, nobody will be upset. It's also considerate to give bellhops and drivers a little something extra for a job well done.