This is a common rounding strategy because it doesn’t consistently overestimate like the grade school rounding strategy of always rounding up does.

That is default IEEE behaviour: https://en.wikipedia.org/wiki/Rounding#Rounding_half_to_even

This is the default rounding mode used in IEEE 754 operations for results in binary floating-point formats.

Though it's definitely a bad default because it's so surprising. Javascript and Rust do not do this.

Not really anything to do with determinism though.