DETROIT - Big discounts helped U.S. auto sales sizzle in July. Toyota, Ford, Nissan and Chrysler all saw double-digit sales gains. General Motors' sales were up 9 percent compared with last July, while Hyundai's rose 1.5 percent. Of major automakers, only Honda and Volkswagen saw declines. It was the best July for the industry since 2006. New vehicle sales rose 9 percent to 1.4 million, according to Autodata Corp.