Also answered by Kyro via IRC... FCS rounds down (as I expected). Thus, FCS is pretty damn useless early on in the game when you've only got 1 or 2 attack points. I had hoped it might be a useful upgrade for my Defenders. Oh well...
edit: Left out one relevant detail, if anyone else is reading... the FCS bonus is calculated on the ship's *total* attack rating, though it is only applied to the first shot in each round. Could be some interesting ramifications there as far as penetrating armor is concerned...