Python 3 has no way to access this implementation of rounding in the
standard library. We implement it here so that we can continue to use
it for grades calculation to keep regrading consistent.
Currently we can't be confident that if we change the rounding behaviour
we won't impact students. We can't be sure that students that were
previously passing wouldn't suddenly no longer be passing. Given this,
it's lower risk to just implement the old rounding strategy here and use
it when we are rounding to calculate grades.
