We are leaving 4/7/07 on the spirit

and I was reading a post on these boards
paying for things on the ship? that said "gratuities are $10 per person per day and 15% on beverages alcohol or any other drinks".Can anyone explain what the 15% charge is and is that included when you purchase soda cards

I knew about the per person per day charge I did not know or have not heard about this 15% charge and my T/A did not mention this.This is our first cruise so I hope I'm not being annoying with questions that may sound stupid to those of you who have been on a lot of cruises but as I said this is our first so we don't know anything about cruising We are learning as we go

Any insight would be greatly appreciated...
Joecat890....