Gas prices take toll on Wal-Mart sales.

CHICAGO, May 27 (Reuters) - Wal-Mart Stores Inc. on Saturday estimated that May sales rose 2.3 percent at its U.S. stores open at least a year, the low end of its forecast, held back by steep gasoline and utility prices. The world's biggest retailer had forecast growth in the range of 2 percent to 4 percent.