Oh! I am very sorry for this! This might misled some people. the "0.05", Should not be there there was some rough experiment I did with that and I supposed to delete the "0.05" afterwards but I forgot. It should not be there please.
I had assumed it was an attempt to round to the nearest 10mV. Anyway that would not really make much difference - given the domain of 0V to 55V in a 10-bit ADC, the LSB equates to just over 5mV.
Unless yo have a VERY well designed and constructed circuit, you will be lucky to get 8 bits of usable data from the ADC (the rest will be noise) which means about +/-200mV is the best you will read.
Susan