What is considered consumer fraud. I know of a 99 cents store in my neighborhood that charges 10% for tax,always has, as oppose to the 8.75%.

This 99 cents store has been charging me and all it''s consumers 10% tax since it''s been here. I live in a mostly hispanic neighborhood and they are taking advantage of it''s population. I confronted the cashier woman regarding this. I bought an item for 2,00 she then told me after tax it is 2.20. I asked her is tax 10%, she replied by telling me it was only "pennies" difference and gave me the correct change. This has been going on for years, is this a valid claim? Do i have chances winning a lawsuit of such? if so, where and how do i begin?