Yes! You can use a coupon for each item. If you get a nice clerk they will run everything you have through and get your best deal. Some of them will even put the VIP 10% discount on top of that if you have a VIP card through ASG, Quilting Society or whoever.
Joann's coupons are kind of a loss leader, since they are only good for "Regularly priced items". They will have items on sale 5% less or so, and then they will not use the coupon.