I’m not sure I understand what exactly do you want to do, or why would
you want to do that.

From: Rounding - Wikipedia :
Round half to even
A tie-breaking rule that is less biased is round half to even, namely:
If the fraction of y is 0.5, then q is the even integer nearest to y.
Thus, for example, +23.5 becomes +24, as does +24.5; while −23.5 becomes
−24, as does −24.5.
This method treats positive and negative values symmetrically, and is
therefore free of sign bias. More importantly, for reasonable
distributions of y values, the expected (average) value of the rounded
numbers is the same as that of the original numbers. However, this rule
will introduce a towards-zero bias for even numbers, and a
towards-infinity bias for odd ones.

The point is that I want unbiased rounding of values that are resulting
from physical measurements; when you can read a measure to 1 decimal,
say 105.5, 104.7, 105.1, 104.9, 104.5, et cetera, and you round these
values to 0 decimals the standard ruby way, then all values ending in .5
will be rounded up; this causes a bias in the average, since actually
chances are equal that 104.5 is either 104 or 105. One way to prevent
this bias is by rounding to the nearest even digit.

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