I bought Target AMEX prepaid card in Super Target using SPG Amex and purchase was NOT classified as "grocery". It was shown as "MERCHANDISE & SUPPLIES - WHOLESALE STORES".
I purchased a diet coke and some mints at a Target on an AMEX the other day to test and that showed up with the above description. Much better ROI if it will show as Grocery for me. Going to test a few others to see if there is a difference.