Rounding issue?

Business created a specific purchase order consisting of material and returned material (credit memo):

- Pricing condition consist in PBXX gross price and NAVS VAT non refundable.

- After entering the material, when we try to simulate and pre save the invoice with MIR7 there is an error which consists in a sold between credit and debit. -0,03 preventing from having the invoice.

I noticed that when the VAT amount in the order is entire like 115 or 1023 system fonctions.

So I checked the rounding in the condition type but with no effect.