Family Dollar review: The cashier and the manager

I went shopping at Family Dollars: located in Chicago store address is 2346 East 79th st story #50. I was $91.69 my total was $77, 00 when I got home an added everything up. I return to the store and the manager added everything up she came up with a total of a $100.00 which is wrong furthermore I wasn't charge no sale tax, so I returned to the store an I purchased a wall picture and I was charge a sale tax.