You're right that lots of folks expect tips here. Restaurants often pay waiters a minimal salary and expect the balance to be made up in tips. Few places add them in automatically except for groups of 5 or more or sometimes more pricey places. Not everwhere are tips necessary like buffets, cafeterias , fast foods and carryouts. Some places have tip lines on receipts because they use the same software for everything carryout or buffet as well as sit down service by waiters.
As for taxes they vary by state and sometimes within states. We don't have the VAT taxes as in Europe so everything is taxed at time of purchase. To further compund it, not everything is taxed and there are occassional sales tax holidays. It gets just as confusing for us natives!
In any event, I hope you're enjoying your visit.