Yeah, my technique is to punch a random number into the machine, if it works then no problem, but if not the cashier will just scan the "store card" after the 2nd failure.

That's my technique too, but when the cashier asks to look up my number I give them 555-1212. That is what fed into my comment. Most people don't care what number is used, but many also don't know that 555-1212 is the secondary information number. This, of course, depends upon their age and geography. This comes up in the friendly conversations that result upon them looking up the phone number.