IHOP will adjust wages based on tips, they try to equal it out to minimum wage. My wife lasted about 3 weeks there. It was also by far the hardest I've ever seen her work, and for context we met in the Army.
My mom was a waitress most of my life and made decent money, so I always tip 20-25% and a minimum of $5 unless I get extra shitty service. Depending on where you and your coworkers ate at, I would say they were just cheap asses.