Rounding errors lead to inconsistent absolute values

Hello. I've noticed that when you run brillo -A 5 and then brillo -U 5 multiple times, the resulting brightness is not the same, it slowly decreases. This is due to the backlight driver accepting only integers, I believe. Not sure if there's a proper way to fix this, but simply using half-up rounding when calculating the final raw value helps in most cases, as testing shows.