OK, I'm out of GUESSes (that last :INTEGER: thing was a GUESS, just tried it and it doesn't liek it (despite what the manual says) - :IMPLIED: should work OK).
Something still sounds wrong then, if your query is definately delivering numbers with decimal places and you are not restricting these in the portlet display options then you should see decimal places (I get 9 decimal places in a quick test of a new query and a new portlet).
I would be tempted to try to create a new 'clean' portlet using your query (or even a new query) and see if you get the same results - just to eliminate the possibility that the config is somehow "broken" in your current one) - you could post the NSQL here, but since its likely to be specific to your datamodel, not sure if that would help.