It's never as simple as it looks. 0.01543236 grains (0.001 grams) seems to be about as high a resolution as you need, as that will show just one physical grain of a rifle powder. However, it isn't always necessary. Much as I love playing with ballistics programs and calculating drops, what they don't take into account is muzzle rise. The program tells you what will happen if you have a perfectly rigid barrel throughout the firing event.
Most real rifles, however, have the bore above the line to the shooter's shoulder so the muzzle tends to rise a bit as the bullet heads down the tube. This is exaggerated by a flexure point formed most of the way to the muzzle that causes the muzzle to tip upward. Whatever phase of the tipping swing the muzzle is in when the bullet exits will determine its exact angle of departure from the shooting position. Typically an accuracy load will be timed such that when the velocity of the bullet is lower and the barrel time longer, the muzzle has used that extra time to swing to a very slightly higher angle of departure and therefore launches the slower bullet on a slighter higher trajectory arc that tends to compensate for greater drop by the time the bullet arrives at the target.
Theoretically, that compensation will be exact at just one range, but it tends to bring all the errors closer. The problem is that how much of that muzzle deflection you get depends on the barrel's length and thickness and height above the stock line into the shooter's shoulder, the bullet weight and the pressure levels in the bore, which cause some barrel distortion and tend to stiffen it behind the bullet like air or water pressure stiffen a hose. So it's a complex interaction and you just have to determine what works for you by testing loads in your rifle. If you can find a good sweet spot over which exact load doesn't matter much at your maximum range, and then load as consistently as you can, that gives you an error buffer that will help with temperature and condition changes.