What does it matter if you are 99kg out on a 63000 aeroplane, it is 0.15%!
Precision is not the same as accuracy. 63149 kg is a precise number, but with standard weights being used for passengers, inaccuracies in fuel gauges and the weighing equipment used to get the basic weight of the aircraft, it is not necessarily an accurate number. Figures rounded to the nearest tenth of a tonne are fine for a large aircraft. If you are doing the rounding yourself then by all means round in the safe direction, but don't lose sleep over a possible discrepancy of 99kg.