We only define 'round3' for PY2 and 'round2' for PY3, and also make sure 'round3' is always an alias of
the built-in 'round' on Python 3; and similarly 'round2' is an alias of built-in 'round' on Python 2.
Thus, for clarity, one can do:
from fontTools.misc.py23 import round3 as round
or
from fontTools.misc.py23 import round2 as round
and be certain that the fast built-in implementation will be used on the
respective python major version.
f742ea07e8