perhaps the lfs are trying to encourage you stock larger shoals - maybe by selling in 5s they are hoping you'll stock 10 instead of 6, hence bigger shoal, hence happier fish...
my local MA also sells in varying umbers, 3,4,5,6,8,10 depending on species.
my local MA also sells in varying umbers, 3,4,5,6,8,10 depending on species.