DON'T ANSWER THEIR QUESTION!

[Duchess]

What do they do with the zip code?? I think the only place I've done this is the gas pump but I thought it was for verification purposes, since clearly there isn't someone there checking your ID.

National Retail Federation says it's done to better know their customers but Privacy Rights Clearinghouse Policy and Advocacy advises against offering it, merchants cannot legally require that of you, the only exception to that is at the gas pumps.

It should be noted this practice is how you come to get junk mail as well.