Bookstore sales slipped 0.3% in April, to $1.01 billion, according to preliminary estimates from the U.S. Census Bureau. Sales for the entire retail segment increased 8.8% in the month. Bookstore sales for the first four months of the year were still ahead of last year's pace, up 3.5%, to $5.38 billion. The increase was below the 9.1% gain posted by all retailers.