From the Python 3.7 docs (https://docs.python.org/3/library/functions.html#round):

The behavior of round() for floats can be surprising: for example, round(2.675, 2) gives 2.67 instead of the expected 2.68. This is not a bug: it’s a result of the fact that most decimal fractions can’t be represented exactly as a float.

Well that is just normal float fun :)

    In [17]: Decimal(2.675)
    Out[17]: Decimal('2.67499999999999982236431605997495353221893310546875')

So sort of round() is working as expected, but the number you are not inputting is not the one you are expecting.