Yes, the answer to your last question is units. But whether your readers will understand simply "please report in units" I don't know. At least you have to say "Please report in units (not thousands or millions)." I think I like TonyK's idea of "to the nearest euro" or "to the nearest euro (not the nearest thousand or million)."
Edited by: VinnyD to give proper credit to TonyK
You know, I don't think I'd understand "units" especially if I were looking at an Excel table. I'd expect "hundreds," even if 001 is not a "hundred."
So, if you gave me a blank Excel table & told me to enter millions, thousands & units, I might be puzzled.
Maybe I'm brain-dead this evening: hundreds 6, tens 7, units 8.
It was certainly customary and prudent (at least in Scotland) in the days when cheques were common to write a fairly large one thus: Pounds, Hundreds, Six....
So you would write 678 on a cheque as 'Hundreds Six, Tens Seven, Units Eight'? I've never heard of this, but then I've never lived in Scotland. I would write 'Six hundred and seventy-eight', but I accept that your method is more systematic.
For big cheques you would write the largest denomination first - and ensure the numerals were written fairly closely together and that the first started as close as possible to the left-hand margin of the box.
'Pounds, hundreds, six, tens, seven - and eight' or 'Pounds, hundreds, six - and seventy eight'. I don't think units were specified, to be fair, on hand-written cheques - but they may have been a few decades before.
Certainly, in the case of printed cheques, even today, this is the format, right down to units - and pence.