Ok, I'll better use the ones I have with lower tolerances then.
Measurement doesn't need to be super exact. I'll use the arduino to measure battery voltage in my UAV ground station. So it's mostly to make sure I don't run out of battery. Because of that I'll try to keep it as simple as possible but also not introduce any unneccessary errors. I'll also measure a bunch of other stuff such a current sensor, clock, timer, signal strength and buzzers and lights to indicate warnings etc. Information will be presented mostly on a 20x4 LCD.
As you probably figured out I'm an arduino newbie and this is my first project, I'm learning as I go along and really appreciate all input.