Yes, the percentages round, granted to the nearest whole percentage number, It might be difficult to display something like 100.002% but this will be over the limit. You should focus on the the MW number more-so than the percentage when setting up modules. There is also a slight discrepancy between EDshipyard and the game when it comes to some percentage rounding, I had a loadout that EDshipyard that said 99%, but the game said 98%, even though the MW numbers were precise matches.
In short, if you have 15.60 MW of power and EDshipyard says you'll be using 15.63, this will be too high for the game as well. Good luck out there!
Edit: Also on percentages, if you ran this loadout in game you might see 100% displayed and should be tinted Red, as in over power limit.
Mmm, that's more or less what I assumed- but it was as well to check- as it'd let me run an extra shield booster. Thanks for the confirmation, I can't jump back into the game to check for myself right now, so it was worth asking here in case someone knew off the top of their head