If you're satisfied with the service provided, leaving a tip of 10% is customary at "genuine" restaurants (those that deliver a printed bill), although it is not required. There is often usually a service charge of 10% included in the bill at restaurants, so you don't need to feel guilty about not paying one. On the other hand, due to the low pay associated with such positions, almost everyone tips. In restaurants located on the street, a tip is not customary. If you're going on tours, you can always tip the tour guide as well. It will be appreciated.