According to a new study by Kantar Retail, which assessed the lowest price available on 21 categories across the edible grocery, non-edible grocery, and health and beauty aids segments, Dollar General took the crown for a third year in a row.

The dollar store widened its lead over behemoth Wal-Mart—which ranked second—with an overall basket price that came in 2.5 percent lower. Last year, Dollar General's basket only beat the big-box retailer by 12 cents. Target's prices were the least competitive of the six stores studied, with a basket that was 52 percent more expensive than Dollar General's.

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Although Wal-Mart built its success and scale on its low-price guarantee, it's ceded some market share to smaller, more convenient dollar store retailers over the last several years. The world's largest retailer has once again been investing in price, as it tries to lure cash-strapped consumers back into stores.

It's also ramped up its promise of offering the best price with its Savings Catcher tool. Savings Catcher allows shoppers to scan their receipts with a smartphone, and then compares price tags to other stores. If a lower price is found, shoppers will get the difference on a Wal-Mart gift card.