A sales tax is expected in most states and is generally fairly similar within each state and almost never come to more than 10%. That also pays for services that most people use.

This extra charge at this restaurant is not common nor is it expected. They also set it at 18% which is a standard tip rate but specifically say it is not a tip. They claim it is to provide decent wages but considering they still allow tips (some places do this but do not allow tipping on top) , that pretty obviously is not true. This is just a bullshit tactic to have prices seem lower than the menu price.