Sales tax can add up, even on toilet paper. That's why a New Brighton grocery store customer balked when she was taxed on a total of $17.29. The Charmin was $12.29, but she said she had a store coupon for $5 off.

"They charged me tax for the $12.29 AND the $5.00 off coupon. So I paid $1.23 tax. Is this legal?" she wrote.

No, according to the state revenue department. She should have paid 52 cents, because she used a store coupon that reduces the taxable amount. With a manufacturer's coupon, the original cost is taxed, so she would have paid 88 cents. Under no circumstances should she have paid more tax than someone who didn't use a coupon.

To read more about sales tax and coupons, visit http://bit.ly/98pxYP.

How do you make sure you're not overtaxed?