Truncate (rather than round) after the thousandth's, i.e. a profit of .00198 = .001. That will give the correct answer, and I suspect is a large part of what makes the site profitable for them. For a 10K users on a good day, that's about 1 BTC.
I am trying to make the results page percentages match my actual results in a spread sheet and definitely having trouble matching them up.
Probably calculating it wrongly, anyone manage to make that work?