You may be laughing, but please take a look at this article:
http://www.forbes.com/sites/adamtan...easons-not-to-give-stores-your-zip-code-ever/
"the California Supreme Court, which ruled in 2011 that stores cannot require patrons to furnish their ZIP code. California later confirmed the ruling in a law that bars firms from collecting personally identifying information during credit card transaction. Courts in other states such as Massachusetts earlier this year have reviewed the issue."
The ONLY reason to provide a zip code is so the credit card being used can be verified as belonging to the name on the credit card. That's why those gasoline pumps require your zip code when you put in the card to pay for your gas.
Other than that, it is unnecessary to divulge one's zip code at a store.