<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def round(self, ndigits=0):
 """ Rounds the amount using the current ``Decimal`` rounding algorithm. """

        if ndigits is None:
            ndigits = 0
        return self.__class__(
            amount=self.amount.quantize(Decimal('1e' + str(-ndigits))),
            currency=self.currency)