does MROUND still have a 'grace range', is it anywhere documented that it has or had?

Question

I stumbled about a funny behaviour of MROUND with Excel 2010: values very little below 0.5 times the 'significance divider' are not rounded down, but up.
E.g. '=MROUND( 5; 10 )' should round up per definitionem, 'midpoints away from zero', but '=MROUND( 4,999999999999999; 10 )' should not, it's below halfway, but does, result 10.

My questions:

was that known and is it somewhere documented?

is it still that way in newer Excel versions, or changed?

if changed: when and why, and where documented?

TIA for any help or hints.

b.