Argus maintains its Hold rating on Dollar General Corp. (NYSE: DG) and said the company has a substantial opportunity to boost sales by opening additional small-format stores.The brokerage said the company's fleet of nearly 12,500 stores differentiate themselves in a crowded retail landscape for providing frequently used items such as milk, cleaning supplies, over-the-counter medicines, beauty aids, snacks and, more recently, tobacco."Management's research suggests that substantially more comparable-format stores could be opened in the U.S., utilizing the company's expertise of operating clean, well-stocked stores in small towns and rural markets," analyst Christopher Graja wrote in a note.via