Know store's strategy when grocery shopping by Mark Albright, Times staff writer So, who sells groceries at the lowest prices? That depends on what you buy and the store where you're most comfortable. Food retailers base pricing strategies on a blend of prices spread across tens of thousands of items. Working on an overall profit margin of 1.5 to 2.8 percent, Tampa Bay grocers shave pennies off hundreds of the most commonly bought items like liquid Tide in the 32 load size to tack the pennies back on items less burdened by price resistance like Cheer in the 64 load size. Grocers don't like to talk publicly about pricing strategies for competitive reasons and to avoid price fixing accusations. But more importantly it's because their job is enticing shoppers to spend more. So the subject runs counter to their low price marketing messages. These days computers and scanner data have made pricing less of an art and more of a science anchored in finding the price that. Walmart and Target sell at the same prices day in and day out yet typically cost about 15 percent less to fill a cart than a traditional supermarket. However, the selection of brands, sizes and perishables is much narrower than a supermarket. . You can save big at Costco, Sam's Club or BJ's Warehouse, but be prepared to pay for membership, buy in quantity, be satisfied with a fraction of the selection, and likely drive a little farther to find one. . Limited assortment grocers like Aldi and Save-A-Lot can be the cheapest choice, but you have to like a store brand that comes in one size. . Dollar stores have plenty of deals especially on paper products and party goods, but pay attention to unit prices. 