JOHNSTOWN, Pa. -- Norma Cain of Jefferson County alerted Channel Six about a major retailer in the Alleghenies who accidentally overcharged her for a converter box.

The Wal-Mart in Brookville charged Cain sales tax on her entire purchase, but according to the Pennsylvania Tax Code, you're only required to pay sales tax on the amount after the discount.

For example, if you purchase a $50 converter box and use a $40 coupon, the store can only charge sales tax on the $10 you pay.

A corporate Wal-Mart spokesperson says, "We were never told how to calculate the sales tax, but we are aware of the problem and have fixed the stores' registers." If you accidentally get overcharged, the store will refund you.

If you buy a converter box under $40, you will not get cash back or a store credit. You can only use one coupon toward the purchase of one converter box.

The converter box coupons expire 90 days after you receive them.