WASHINGTON — U.S. businesses added to their stockpiles at a slightly slower pace in June compared with May, possibly reflecting weaker sales in the past two months.The Commerce Department said business stockpiles increased 0.4 percent in June on a seasonally adjusted basis after a 0.5 percent gain in May. Sales rose 0.3 percent in June, matching the May increase. Sales have slowed after rapid gains from February through April.The sales slowdown was also evident in a separate report showing that July retail sales were flat. Most analysts say they think solid job growth will give a boost to consumer spending and the economy in coming months. Many foresee an annual economic growth rate of around 3 percent in the second half of this year.