Inspectors from the Office of Consumer Affairs fanned out across the city and found that 52 percent of the supermarkets they surveyed were in violation.
City inspectors surveyed more than 700 grocery stores and discovered that many weren't abiding by a rule requiring a price tag for every item on the shelf.
In many cases, they were overcharging at the register and collecting tax for non-taxable items.
Others rang up items at the wrong price. Nearly half didn't calculate taxes properly, including wrongly including bottle deposits in an item's taxable price.
What's worse, Consumer Affairs Commissioner Jon Mintz says that in the city's poorest neighborhoods, two out of three supermarkets were in violation.
And believe it or not, it happened to Eyewitness News. Reporter NJ Burkett went inside to buy a Diet Coke for his photographer. The price on the shelf said $1.49. But according to the receipt, he paid $1.69 -- overcharged by 20 cents on just one item.
And the nickels and dimes can add up fast. The sheer volume of violations was so alarming that the number of inspections is being stepped up. Mintz says his department will double the number of inspectors next year.