As far as I know, across most of the United States, tips are the main source of income for waitstaff. For the most part, waitstaff are paid well under minimum wage. In some cases, $2.00/hour. Thus, the reason for a 15% to 20% tip. I usually start at 20% and work down. Most say only tip on the product served and do not include the tax. I tip on the total bill because at that point, your only talking a few dollars. (re: Bill without taxes, $100. Total with taxes, $108. Tipping at 20% on $100, tip is $20. Tipping at 20% on $108, tip is $21.60). Not much of a difference.

Also, if you do a tour, even though it is not required, they do push a gratuity. Do you need to do 20%? In my opinion, no. This is not a dinner. Some tours could be $150 per person. If your a family of four, a 20% gratuity on $600 would be $120. That would add up fast if you were to do several tours. Remember this, if you are on a tour, there may be up to 60 people. That is why I only tip up to $20 per person, if an only if, the crew or operator did a good job. Some people don't tip at all. I have witnessed crew members on a boat trip bend over backwards serving "high maintanence" guests. Those guest walk off without even saying mahalo. That is rude.