Relogging doesn't change anything for me. And I really don't think it's a rounding issue, it always gives me the same amount of silver in copper even if it's off by 1. Here's some screenshots to illustrate:
Here I'm about to sell a diamond for the listed price, notice it will give me 2 silver, but 0 copper:
And now I sell 1 of them and look, I get the 2 copper instead of none:
Now I'll sell all 19 of them (I deleted all my money first) and again, I'm given same amount of copper as silver when I should be getting 0 copper:
(split post due to 4 image limit)