Petco, a pet supply store, was fined more than $13,000 for scanner violations.
Inspectors at the Wisconsin Department of Consumer Protection say Petco stores had an average error rate of 6.5 percent.
Stores cannot have an error rate higher than two percent.
Inspectors say they're monitoring the problem, and their advice to consumers is to check your receipts.
The average overcharge was $2.65.
Officials at Petco say they are happy to get the matter resolved in a way that's consistent with their policies and practices.