"I really hate this as they calculate the total including the tax-you should not have to tip on the tax."

Yeah, actually you do. Plenty of tight asses try to skimp on the tip this way, but you tip on the overall cost of the meal.

In the case where you felt jaded by them adding a gratuity, you should have mentioned this to them instead of talking about it with people on a website. In the end, it was shown on your bill. The onus is on you to review your bill.