Most stores will ask for your zip code when completing a credit card transaction. Without blinking, we give our five digit numbers readily. It will be a surprise to many that zip codes are not needed for the credit card transaction to go through. The cashier is taking the data as part of a marketing strategy-yes it is only collected for future marketing campaign.

Adam Tanner wrote on Forbes how when he refused to give his zip code to a Mob Museum cashier in Vegas-the cashier was surprised and she also said, that nobody has ever refused to give their zip code! Nobody, perhaps because we are unaware that zip code data is being collected for marketing purposes.

The retailer already has your name when you are shopping in their store. Handing over the zip-code means that it will be able to locate the exact address of where you live. And then begins the never ending flyers and mails of various stores, parks, restaurants, museums, bakeries, and all those places you have swiped your card and handed your zip code

You are not required to give any personal information, show your ID when buying at a store. It’s a different story when the back of your card is not signed and the clerk just wants to verify your identity, though.

CreditCards.com said:

Consumer advocates advise just saying no when asked to give information beyond what is necessary for a transaction -- an address for shipping purposes or a Social Security number if you're opening a line of credit, for instance.

You don’t have to give your email address as well because the retailer is collecting your details only to send store promotion emails. Remember, the stores want to get to you even when you are not shopping –they are simply collecting personal information for their marketing purposes.

Beware of what you do, if you want the hundred junk mail and discount coupons then go ahead and share your information-but know that zip codes are being asked not for the transaction to go through.