I have always been, I think, a reasonably generous tipper. I almost always leave 20% of the total (including tax) in nice restaurants, and often push it up to 23-25% in places where I am a "regular" and get treated especially well. In very casual coffee shops, I usually tip 15-18% of the total bill.
I have recently been told that tipping on the tax is excessive and unnecessary. Upon calculating it out, I realized that a 20% tip on the bill including tax, is equivalent to about 22% of the food/drink portion of the bill. What do you folks do...do you tip on the total bill including tax, or on the total without tax? Just curious!