Hmmm, I just bought $1000 worth of cards in early Dec and my receipt was for $900. I bought more a week later but forget exactly how much.
And not all the staff believed they could be stacked. Especially the second time I bought, they were all like no, that definitely won't work and wanted me to prove I had done it the week before, seemingly to fix it, lol. Finally got them to just try doing it and it worked just fine as I said it would, that manager was very surprised, lol. I was getting a bit frustrated with them, thought!