I've tested only with freehand and symmetry tool basic brush, the round is allays to less. The worst case is that it is really noticeable in some cases as it nearly remove near 1 integral value from size depending on brush size.

Reproducible: Always

Steps to Reproduce:
1. put a brush in 1.5 size for example
2. activate erase mode 
3. deactivate erase mode

Actual Results:  
the size is rounded

Expected Results:  
no rounding 

I know is a minor problem but is really annoying  in some cases like BW fine line art as it can change a lot luminance in some cases (from 1 produce gray lines compared to 1.5).
You can correct the size, but some times it can pass unseen and undo do again is necessary.