There are at least three ways to figure this out using the basic 15 percent tip.
1. The easy way is to double the tax which would be more than 15 percent. So then, the total you would leave amounts to $13.00.
2. Next you could leave 15 percent of the food total which would be $1.50, bringing the total you would leave to $12.50
3. Last and probably the one most people use is to add 15 percent - depending on service you could leave more or less - to the entire bill which means your total would be $12.65.