Rounding up and Down
As far as I know, the Serial.print (or println) does rounding up and down. All you have to do is take a float variable and do Serial.print( value, 1);

Without extra parameter, the default is choosen, which is 2 decimal digits: Serial.print( value, 2);

Why do you want to shorten the bytes over the Serial ? You can just as well send two decimal digits and process the value in Python.