Why Doesn't My Debit Card Work At Wendy's?

This is an issue I've been having for over a year now.  Anytime I eat at the neighborhood Wendy's near my job/home, their registers are unable to read my debit card.  Now keep in mind, I use my card on a daily basis (I never carry cash), and I never have ANY issues getting it to work.  Wal-Mart, Food Lion, Movie Theaters, gas stations, McDonalds, NEVER AN ISSUE.  Yet soon as I get to Wendy's, the card doesn't read.  Hilariously enough, one kid tried to get lazy and say my card was declined.  I laughed at him and said "nah homie punch the numbers in", at which point the transaction went through.  What's the issue here?  They're registers seem to be relatively new.  They even have the lil' full color LCD's on the front that display your order and price.  Yet they can never get my card to read.  Luckily for them, I love their chicken nuggets enough to put up with this rather minor inconvenience.