TJX Cos., the Framingham company that operates T.J. Maxx and Marshalls, reported that September same-store sales rose 6 percent when compared to the same month a year ago. Same-store sales, sales at stores open at least a year, are considered a strong measure of a retailer’s performance. However, the company also estimated it will record a one-time charge in its fiscal 2013 third quarter which will maintain its previous guidance for earnings to be near the high end of between 56 to 59 cents.