So, supposedly, we should pay 10-15% of the "before Tax total" for tips.

But, restaurant always use the "after tax total" to calculate it’s suggested tips.

Are restaurants misleading ? Misrepresenting the fact? Can I sue/complaint restaurant doing about that.

Calculate the tip on the amount before the tax and before any coupons or discounts. It makes no sense to give the server more money because the governor of the state is greedy or the city / county imposes additional tax. I do at times tip based on the full amount if I felt if the server deserved a bit more than the standard but not enough to bump it up to 20%. As for as the suggested tip, you cannot sue them because it is suggested. If you complain, I doubt if it would go anywhere.
As for those that are saying that they standard tip is 20%, those answering are food servers, don’t give that much or more unless they deserve it. z