Eighteen Daiei Inc. supermarkets subjected consumers to double the correct level of consumption tax Tuesday, as cashiers failed to operate cash registers properly following the introduction of a new pricing system, the company said.

The mistake resulted in 763 customers paying a total of 59,388 yen too much, Daiei said.

The company will refund the money if customers take their receipts back to the stores or if they can supply other data that confirm their payments.

On Thursday, the government introduced a tax rule change under which retailers must include the 5 percent consumption tax in advertised prices.

According to Daiei, the 18 outlets in eight prefectures failed to modify their cash registers and cashiers forgot to undertake the necessary procedures to implement the change. This resulted in an additional 5 percent charge being levied on amounts that already included the tax.

Double-charging episodes occurred at 59 convenience stores operated by East Japan Railway Co. on the first day of the new tax rule, and at 22 outlets of McDonald's Co. (Japan) on Monday.