SAN FRANCISCO (Reuters) - Wal-Mart Stores Inc (WMT.N) expanded its service that allows shoppers to pay their household bills in person to all its U.S. stores.

The discount retailer, which has been expanding the financial services it offers lower-income shoppers, began offering the service, for which it charges a fee, in some of its stores in February. It is now rolling it out nationwide in all of its Walmart discount stores and Walmart Neighborhood Markets.

Wal-Mart said the walk-in service is geared toward shoppers who do not use checking accounts and often pay bills in cash. Most banks offer online bill payment for free.

Wal-Mart spokeswoman Linda Blakley said it is difficult to tell if the retailer is attracting new shoppers by offering the service because customers pay for bills with cash.

But she said it was designed to fill a need among its existing shoppers. According to research commissioned by Wal-Mart and conducted by Aite Group, paying bills in person is common among a large segment of Americans who make less than $45,000 a year.

The bill payment service is being offered through Fiserv Inc's (FISV.O) CheckFreePay and through MoneyGram (MGI.N).

Customers pay 88 cents for standard bill payment with CheckFreePay, or $1.88 for next-day bill payment. Same-day bill payment through MoneyGram starts at $4.50, Wal-Mart said.