You can bind the controls to your keyboard if that’s the case. There are likely keys already defined for it.
I don’t fly the A320. Not an airliner guy. But it gives me 1 degree increments on headings on every single plane using my mouse knob. Don’t know why it would be different on that one.
I did have the 10 degree issue before though, and it’s because I had my heading commands also bound to another external controller (I had HDG up / down bound to keys on my old Nostromo n50 pad). Once I unbound, the problem went away and has been gone since.
Nowadays I use the Logitech Multi-Panel, so it’s no longer an issue either way, but I still use the mouse wheel occasionally because it’s quicker sometimes, and never had the 10º issue since.
EDIT
I’m in a long IFR flight in the TBM atm, but I’ll load up the A320 once this is done and test it out to make sure.