It's only tangentically related, but my friends and I went out, and I paid on my credit card (and they all handed me cash) and we had this long fuss about whether I'd tipped or not, because you can write the tip underneath the subtotal when you pay on your card, and then write in the final total. I waited until they left, then asked the waitress to be sure.

...they were so nice to us. My friends were loud, but we weren't rude. And there *were* seven of us. XD