Wrong weighted grades?

I noticed that in the progress tab, in the Grade Summary section.
As you can see in the picture I got a row with a grade of 70% and the weight is 5%. I assume that Openedx uses the Away From Zero rounding method. The weighted grade should be Math.Round(0.05 * 0.7 * 100) = 4%, but in the picture, you can see it is 3%.
I think this is because of the floating point number problem, which 0.05 * 0.7 * 100 = 3.4999999999999996.
Is this a bug or I misunderstood something?