WASHINGTON (MarketWatch) — Sales at U.S. retailers increased 0.2% in July, the fourth straight monthly gain, the Commerce Department estimated Tuesday. Ahead of the report, economists surveyed by MarketWatch expected total sales to rise 0.3%. But details of the July report were stronger. Sales rose an upwardly revised 0.6% in June, compared with the prior estimate of a 0.4% gain. Excluding the 1.0% drop in motor vehicle sales, retail sales rose 0.5%. Economists had expected ex-auto sales to rise 0.4%. Core sales, excluding autos, gasoline and building materials, rose 0.5% in July. This is the strongest gain this year.