Looking at restaurant credit card receipt.

Base $42.19 Tip 20% (8.20) 25% (10.26) 30% (12.31)

Food $37.74
Tax 3.02 8%
Surcharge 1.43 credit card 3.5%

A couple problems for me. In my world, The base for tipping is $37.74. In my world, 10% is a reasonable tip for the under performing server that is so common. 15% for doing the job efficiently. 20% where I am or person with me is a regular. There was a joint in town where the suggested tip listed 20% 30% and 40%. They were out of business within eight weeks. Population of town about 30,000 in northern CA.