MROUND Function

The MROUND returns the number rounded to a certain multiple.
In Excel 365 this function is still available for backwards compatibility.
This function has a rounding bug that has always been there and will never be fixed.

Known Bug

There are known bugs when the "multiple" is not a whole number.

mround(1.05,0.1) = 1.1
mround(2.05,0.1) = 2.1
mround(3.05,0.1) = 3.1
mround(4.05,0.1) = 4.0
mround(5.05,0.1) = 5.0

mround(6.05,0.1) = 6.0
mround(7.05,0.1) = 7.1
mround(8.05,0.1) = 8.1

mround(31.05,0.1) = 31.1
mround(32.05,0.1) = 32.0

mround(1.05,0.2) = 1.0
consistent

mround(1.05,0.05) = 1.0
consistent

Should Use

ROUND(number / multiple, 0) * multiple
(6.05 / 0.1, 0) * 0.1

Best to not use decimal fractions
It is more reliable to adjust the parameters so they are integers and divide the result accordingly