> I don't know how taxes work in Europe, but in the US being "essentially" correct is not good enough for the IRS.

It often is. On multiple years they've found errors in my return, and they just fix it for me and bill/refund the difference (usually a refund).

And obviously, the IRS is not going to quibble over 7 pence, given that you round up/down to the nearest dollar anyway.