It would be rude to just leave them in the same way if would be to leave someone who is talking to you, here’s what I would do “Just the plastic bag for you” “Yes” “Would you like to pay with cash or debit” “Ddddddd—-dddeeee” “Would you to sure debit card” “Yes please” Then you dash off for the card machine I think the rule of act like they are speaking fluently still applies here, if someone was speaking would you get the card machine half way through there sentence, probably not right