Wrong result with negative tax

Wrong result with negative tax

Hello Zoho team.

I read forum treads about negative taxes but I don´t find an apropiate fix.

This is the right way:

Subtotal ................................ 100,00€
IRPF (-15,00%) ..................... -15,00€
IVA (21,00%) ........................ 21,00€
Total ...................... ................106,00€   [100-15+21 or 100 +(-15+21)]

But if I create a Tax group including IVA and IRPF, then the count is wrong:

Subtotal ................................ 100,00€
IRPF (-15,00%) ..................... -15,00€
IVA (21,00%) ........................ 17,85€
Total ...................... ................102,85€   [(100-15)+21]

How can we doing correct in Spain?