Retail sales figures released on Thursday show that buying has not slowed down even as higher gasoline prices are having some impact on shoppers’ habits. Sales increased in April across the board, from luxury retailers to discount stores. Luxury retailer Neiman Marcus saw its sales in its 37 stores increase by 12.5 percent. Department stores such as JC Penney, Federated, and Nordstrom all reported better than expected sales in stores that had been open for over a year, and all of these department stores increased their forecasts for first-quarter earnings. The impact that higher gas prices are having on shoppers’ habits - what they are buying and how many shopping trips they are taking - was revealed in data released by Wal-Mart, the largest retailer in the United States. Wal-Mart figures showed that their customers are not coming to their stores as often, but they are buying more when they do go shopping. The data also showed that Wal-Mart customers are buying more food than general merchandise. Overall, Wal-Mart’ sales increased 0.9 percent in April, with Sam’s Club stores showing a 4.9 percent increase and an 0.1 percent increase at Wal-Mart stores.