Your data are making me pull out hair; I'm used to recording every hit for some more in-depth statistics :I

I can come up with a zany but plausible double-rounding scheme where a skill's potency is translated into an integer damage and then given the ±5%, but that doesn't prove to be anything like a solution for these strange results, because even if that's what happens, the numbers are still too far off for it to work.