I read the following in the comment section of Southern Savers.
"they are doubling all over charleston sc up to .99 will double - the catch YOU have to tell the cashier to double each coupon. Or so I was informed - after I called, talk to customer service at the store asking for the rules.......Then I was told that I had to bring a competitors ad stating that they doubled coupons and let the cashier know for each coupon i wanted doubled."
Please note, there was difficulty with the transaction and Walmart refused to return the coupons. Other results with doubling coupons were successful though. Some Walmarts will not do price matching and doubling together (one or the other, not both) Also saw these locations are doubling: