Remember that you've already paid for his gas by hiring him as a driver so as far as tipping....tip for service and not GP. Ask yourself a few questions before tippin such as how many bags did you have, were they big and heavy and how helpful was the driver with your bags. How many stops did you make? Was the driver conversational? Did he make you laugh or share some Jamaican history with you? My advice is to not have a set amount in your head and see how the driver treats you and then do what you feel is right. You also have to remember not everyone has the same budget. Some can afford to tip more than others so do what you are comfortable with.