This is YMMV because it requires a unique coupon code that Target sent out in physical mail that says "Free $25 Target GC with household essentials purchase of $75 or more." It then has a barcode and a unique coupon code you can use online. What's great is that, you can combine this coupon with their current promotion where you get $15 or $20 back in GC when you order select household essentials of $50 or $75 respectively.
In my case, I placed an order of $76.80 with $40 back in GC ($25 & $15 GC). Even though my order was $75 or more, adding my unique code for $25 reduced the other promo GC from $20 to $15, but this is still an amazing deal. If you haven't checked your mailbox, I highly recommend you do and don't throw away if you see something from Target. I almost threw away mine as I normally don't bother keeping stuff like that. Good luck!
UPDATE: Several people reported that they could not stack the deals in store, so this may be online only. With that said, at least one user reported that his store was nice enough to manually issue the GC, so you could always try and see if they'll help you.