If they used plan credits, you'll receive a receipt (at TS locations) listing the covered items at $0.00 each.
Note that you will first receive a normal itemized receipt. The "zeroed" receipt will come after they actually run your card.
If you're concerned about the possibility, do not have charging privileges added to your KTTW card. Then they will have no choice but to take meal credits. Of course, you then have to carry around cash or a charge card...