If you go to the restaurant tax apply after deducting discount? and gratuity and or tips are taxable?

Most restaurants apply sales taxes after the discount. Gratuities are tips, and they are taxable in the US. Restaurants report the tip income from credit card receipts and estimate the cash tips. The IRS sometimes challenges wait staff at higher end restaurants about under-reporting tips. Personally, my wife and I tip on the total amount before any discounts.