How much do you tip?

[taylor]

I recently paid dinner for two of my customers. One of them saw the bill and said I was tipping too much. And then he told me I should only pay a tip based on the subtotal without the sales tax. Then my other customer chimed in and agreed with his colleague. I generally tip 20% of the total bill including sales tax as long as the service is good. I thought I was the normal one. I think I'd prefer gratuity included in every bill, too much second guessing.