Many of our guests are coming to the United States for their first time and often ask us about tipping their taxi driver, waitresses or maids. Although tipping is not customary in many countries around the world, tipping is standard in the United States. Below is a very simple guide on tipping along with a link to TripAdvisor's guide to Tipping and Etiquette in the United States. Both will come in handy during your stay.
Taxi Driver:
10% - 15% of fare
Waiter/Waitress:
10% - 20% of bill
Housekeeper:
$2 - $5 per day
Bell Hop:
$1 - $2 per bag
Bartender:
15% - 20% of bill or $1 - $2 per drink
Valet:
$2 - $5 depending on location
http://www.tripadvisor.com/Travel-g191-s606/United-States:Tipping.And.Etiquette.html