MURRYSVILLE, Pa. -- With her newly-arrived settlement check now blown-up and laminated, consumer advocate Mary Bach and her husband, Lenny, celebrated their most recent victory against a retail pharmacy giant over a billing problem.

"I want people to stand up for their rights, and again, I call this a message lawsuit hoping that my efforts will educate people about their rights and what the law actually says," said Bach.

When the Bachs went shopping at a Murrysville, Westmoreland County, CVS store last month, the sales tax was calculated incorrectly.

The Bachs purchased two digital television converter boxes at $40 apiece.

They had two $40 government coupons, so there should have been no sales tax on the purchase because in Pennsylvania, the sales tax is calculated after a coupon is deducted.

Instead the Bachs were charged for the full amount, with the store manager refusing to correct the mistake.

They sued the retailer for $100, plus court costs.

CVS settled for the full amount over the weekend.

"Through their corporate counsel, they came just short of thanking me for the lawsuit because it caused them to look internally, realizing that possibly I was correct, and they discovered a nationwide problem in their system," said Bach.

CVS admits all of its stores may have been overcharging customers on sales tax for the converter boxes prior to the Bachs' lawsuit.

Bach also successfully sued Wal-Mart and K-Mart over billing and sales tax issues, making national headlines every time.