10% demand for tip

10% demand for a tip I was at mug and Bean with my family today to have lunch. There was 10% tip written on my slip in addition to what I need to pay for my food.I rounded the payment and ignored the 10%, but the waiter insisted to pay 10%. I then I asked the waiter what is 10% is about. She told me is for paying for her salary. I total refused and told her to go and ask the manager for the salary.