See Box 1 in your W-2 form. It says: ” Wages, tips, other compensation”
If person suppose to show his/her tips, when files income tax return, it must be legitimate to receive it.
In some restaurants they include waiter’s tips in a bill. Other places just put in writing suggested %% for tips.
Some owners pay delivery boy cash (less than minimum legitimate wages) and tips are actually what they working for.
18 years ago, when I came to USA, I received from Jewish Community Services a brochure “Welcome to America”.
One paragraph was about tips – who we suppose to give (waiter, delivery boy, taxi driver, barber…) and how much, who we should not give ( UPS driver, clerk in governmental office…).
So, I assume it is nothing new for someone, who was born in America.