Questions about numbers on Z list from a cash register for a restaurant

It's a restaurant, the 'net amount' doesn't equal the 'gross amount', and the difference doesn't tie to any other number. What is usually in the difference? Also what the total amount by department supposed to equal to? It doesn't equal to net or gross. 

Btw, could anybody give me some direction where I can find the sales tax rate for restaurant food and liquor sales? It's in Kane county, IL. 

Thanks a lot.