[GAMEPLAY] Healing is not a flat amount

I've seen this on people such as Nami, Nidalee, and Sona. When I would heal somebody, it would not be the same. It doesn't occur all the time, though. For example, as Nami I would heal myself for 101, but sometimes I would heal somebody for either more or less by one or maybe even a bigger difference. And no, it did not bounce.

Because of this, I went into a custom game mode (Summoner's Rift) with a friend and tried out to see what was causing it. Also didn't put any bots because we could just have the tower or dragon hit us. We didn't take any runes or masteries and we didn't buy any items like spell vamp. I went as Nami because she's cool and my friend went as Galio because of his MR shield. First we decided to see if it was because of level difference because usually supports like Nami are underleveled and that was not the case I guess. So then we decided to see if it was MR, and I'm still unsure if that's the problem but when Galio would shield himself, and I healed as he had the shield on it would SOMETIMES he would be healed +1 for what it actually should be healing him for. Also getting hit by drag and shortly after getting healed would again, sometimes be healed for +1. So I'm still not sure what the cause is, or how to fix it.

Sorry for the long post with no screenshots or a video :(