Some may argue this, but I would have no problem at all putting five Cories into a ten usg if it is well maintained and cycled. Frankly, I might add more after awhile--also with appropriate water and tank maitenence.
Ten usg is often recommended as a breeding tank for 5 Cories. If you put an an aeneus lady and some fellows in a 10 gal., you will eventually have more.