Complete numbers is not correct

I have a problem with my number completion afther the comma

when we want to put in this number 6.582,6446 to make that the result included VAT 7965.00€ as result.
We have as result 7964,99

but when I change the decimal numbers from 2 to 4 in the database, is it not working
Its still take count of 2 decimals afther te comma.

What can I do to fix this issue?

InvoicePlane currently does not support more than 2 decimal places. You would have to change a lot of code to make more places work.

Is it not possible to change the caculation from a number 1234.1234 and as result 1234.12 ?

No, because the rounding is hard coded.