Not always true… It\s a bit more complicated, because here are MANY rounding precision setups - invoice, VAT, payment tolerance, ForEx rates and maybe more, I can\t be sure I remember them all by heart now.
Setting all these up is a little bit messy process, they can come into conflict sometimes - that is, somewhere rounding is allowed, and somewhe it is set to zero, and in such case the msg quoted pops up.
It looks like setup problem, not direct and errorenous usage of rounding func somewhere in code, as mohana suggested earlier…