I suppose you may indeed be correct. I always assumed not as it's not like they give you a donation receipt like when you directly donate to a charity. Now that I think of it, however, the donation itself would be itemized on the receipt and could therefore be used as proof in a personal audit. I just never really considered it as I just donate like 2 bucks here or there via this means.
I suppose this also might vary in different jurisdictions.
End of story, I'm willing to admit that I may have been misinformed (AKA wrong) myself.