5 in a 5gallon tank= cannibalized mice. Not a good idea if you actually wanted to use the mice in the future. That size of cage stresses them out and stress means that they aren't eating and gaining weight. You "might" be able to put one mouse in that size of tank. The amount of ammonia they produce would probably kill 5 of them pretty quickly.

I keep 1.2 and "sometimes" 1.3, if I have to(when I need babies), in a 10 gallon. For the ones growing up to be fed off, maybe 8-10 are kept in a 10 gallon. But since they aren't there for that long and they are pretty small, they all do fine. If you are planning on breeding that many in that small of a tank, you will have eaten babies, stressed out momma mice and probably eaten males as well. They like a big enough enclosure to spread out their babies if need be.

If you would like a cheaper solution, you could keep 1.3 in a big sterilite container(50qt) and replace the majority of the lid with hardware cloth(found at Home Depot and Lowe's in the fencing department). Then, just use a soldering iron to melt a big enough hole for the water bottle spigot and you are set. I have one momma mouse and her two(whoopdeedoo...) babies in a small 16qt? one and she is doing well. If you keep them busy with shredded newspaper, paper towel rolls and all sorts of little things like that, they won't feel the need to try to chew out.

What are you feeding your mice and what bedding are they kept on? I feed mine Mazuri Breeder Mouse lab blocks(from feed store) and keep them on kiln dried 100% hardwood shavings(some pine, not all, found at Tractor Supply Co.). Hope this helps