How to create an "increase x percent of order" button

I want to create an button that can increase, for example, 10% per an order for each bill and allow to print it out. Can anyone help? Thanks so much

Imagine 10% is a tip?
Try the search option on the forum - top right looking glass icon.
This is a subject that is discussed allot. Generaly calculations are used.

Thanks. I will find.