Currency rounding difference (Dynamics 365 online, version 9.0)

I have a quote product where my Amount is €100,50

The tax field is calculated by a business rule (21%) and shows €21,11 (but really has a value of €21,105)

Now the Extended Amount shows €121,60, instead of the expected €121,61.

Why is the rounding of Tax and Extended Amount different? And is it possible to change either one? And how?

(All the fields are set to currency precision).