Having x10 divider arduino resolution would be 50 mV, or about 51 - 49 / 0.050 = 40 counts.
I'd simply do oversampling, suppose you don't need very high speed update.
Summing 256 values in one "long", than shifting right on 4 bits (you can divide by 16 - same thing) ,
you can get x16 times better resolution, or 640 counts per range.