Not according to the United States government, which is why your server is paid $2.13/hr instead of $7.25. A server has a minimum expectation to take care of a customer, and in doing so, should receive a tip of no less than 15% of the pre-tax bill. Not getting good service? Ask yourself if you've eaten there before and how well you tipped. I usually look like a bum, even on my first trip to a restaurant, but am generally given good to outstanding service. Twice I was given luss poor service. The first time, my family and I walked out without even ordering. The last time, it cost the server their job.
But even basic service, making sure everything is okay, drinks need refreshed, etc, is cause for a good tip. I generally tip 20% to 30%. I've eben tipped 100% if the service was good even though I was only having coffee.
When I started eating in restaurants, the normal tip was 10%. It's hung at about 15% for most of the last 40 years, although some now include the tip in the bill for larger parties.
If you get known as the cheapskate that still thinks a quarter is a good tip for a $20 bill, though, I wouldn't expect great service.