I believe you are seeing a long standing Quicken bug, or a variation of it (and I agree with BobL that it may be related to rounding, but I think that unrealized gain computations also play a part).
I typically see the bug when I display something like the Net Worth report, with some interval other than "None", with the Customize option "Account detail" selected.
When I create such a report, I see those very small values (nearly always between -$.06 and +$.06) for some securities I no longer own; usually starting in the period when all shares of the security were sold (or removed) and continuing through the most current period in the report.
When I customize the report NOT to include unrealized gains, the small values disappear from the report. And if I use an interval of "None", the small values do not appear in the report (regardless of whether I display unrealized gains).
I believe the problem has been around for a decade or more; I still see it in Q2019.
Given the tiny $amount of the errors, I have never worried much about the problem.
[I don't recall ever having seen any of those small erroneous values in an Investment Asset Allocation report/graph. As far as I can tell, all the securities that appear in my Asset Allocation graph/report are securities that I still own.]