I go in half grain increments. 5 round groups. I find out what's closest, then work in 0.2 grain steps.
Say we're starting at 15 and working up to a max of 20
15 - 15.5 - 16 - 16.5 - 17 - 17.5 - 18 - 18.5 - 19 - 19.5 - 20
Then, if my best group was say 18 grains, I'd do the following
17 - 17.2 - 17.4 - 17.6 - 17.8 - 18 - 18.2 - 18.4 - 18.6 - 18.8 - 19
Out of that, there will probably be a spread of 5 or so charges that don't seem to make any difference. Take the middle one, and that's the load I go with from there on out with a particular bullet and powder.