I wouldn't make the assumption that skill level and enthusiasm level use the same rounding methods, again, unless I've missed something the BB's have said. I understand why it would make sense to make that leap, but that assumption could very well be incorrect.
I'm sure there are mathematical ways of finding out which rounding method is being used, I'm just not smart enough to figure it out. For example, if someone does have an enthusiasm of 12 going into a game it is likely a very low 12 (close to 11.5 or 12.0), and after TIE'ing that game, if it goes to an enthusiasm of 15, then we know .5 is rounded up because the 12.0 should go to 16... (although that's assuming it is increased by 1/3 and not just 0.33).