Just download the Groupon app
Chances are you'll spend $10 at Target at some point in your life. If so, you might as well save 50% off a $10 purchase, right? $10 Target Mobile Card for $5
Just download the Groupon mobile app for free to get it. You'll need your mobile device in store to redeem the discount (or enter a code online), but assuming you're putting the Groupon app on your smartphone, that shouldn't be a hassle.