Earlier quoted context omitted.
In a few stores here in Australia, I am asked for my post code (or country of residence if no post code) by the cashier when ringing up a sale. Predominantly at tourist/tour related points of sale, but I've also had it an electronics and white goods stores. No idea if the operator is also recording gender and perceived age group etc., but I do know that on most occasions, you can opt not to answer the post code quest…
I'm not sure if it's true, but a friend once told me the reason a store asked for your zip code was to see if they had a large audience coming from a certain area. This let them know other locations to possibly open other stores.
IE they keep the last 4 digits of your credit card, combined with a post code you have a unique id.