I've never seen $5 Disney cards but earlier this year, I bought Disney Gift Cards at Lowe's Home Improvement where you can choose the amount you place on the card. I placed $68 on one card to cover my parking expenses for 4 days and then just kept that card in the car. Worked like a charm. There are probably other stores where you can do that or maybe try the Disney store online.
All of the Disney gift cards I've seen that let you choose your own amount have a minimum requirement of at least $15. I don't think you'll be able to do $5.
The Disney store website says that Gift cards can be purchased anywhere between $5 - $1,500. I don't see an option to buy online so you may have to go in store.
Edit- did a little more research and the minimum is $25 to purchase online. Maybe they haven't changed in FAQ section. But doesn't hurt to call your local store to find out for sure.