Rounding problem

Hello,

i've this function

round(sum(stuffs.total), 2)

result is 156,25€, now i need the 22% of this so

round(result of previous funcion * 0.22, 2)

result is 34,375€

why does it round to 34,37€ instead of 34,38€?

If i create a number field, write 156,25€ and use the same function it works properly, but it doesn't with a rounded sum that gives the same number?

Thanks