I would hazard a guess that you probably know the mass of fuel on board to greater precision than the rest of the aeroplane and its cargo. Hold baggage is generally weighed but passengers (and crew) and their effects aren’t.
If an extra tonne is going to take you off the end of the runway, then maybe you should be landing somewhere else? Despatch LW check before aviating should see to that?
Getting the aircraft down in the right place at the right speed is more important. If you take the same aeroplane at slightly different weights but land it at the same speed (which you calculated was OK), how does it affect the stopping distance...?