4 digits does not a rounding error make when the autotracker displays only 2. if today's gain plus ytd = +xx.0049% you get 0.37. if it = xx.0051% you get 0.38. all your (pretend autotracker money) is still there. the difference is pennies in how it is represented.
An old programing trick was to have the rounding alternate at .005 one time up the next down. That could explain why some have a .37% and other got a .38%.