Did you try it? It has everything to do with how numbers are represented in floating point. There are numbers that can be exactly represented in floating point where the rounding is ambiguous, e.g. printf "%.1f", $_ for .25, .75, and a round-to-even-last-digit rule could apply, but in fact perl relies on C's printf(), and the SUSv3 standard says only "The low-order digit shall be rounded in an implementation-defined manner." Depending on how you interpret "rounded" in that sentence, you may not even be able to count on it rounding .24 to ".2".

In point of fact, I don't know of any system that fails to round at all, but do know of some that do not consistently either apply or fail to apply a round-to-even-last-digit rule.