This module is doing it wrong!
First of all: I didn't use this module myself, I'm just rating it from what is told in the documentation.
Jess Robinson has reported this before, and the author added a formatting option then (currency_set), but number formatting is *in no way* related to currency. Instead it is only the (user's) locale setting, that defines formatting, so the bug is still unresolved.
I would really like to use this module myself, but the way it works makes it virtually useless for me. What's even worse, a couple of other packages use this package and inherit its kaputtness.