I am not aware of all your requirements, but this will be fairly robust.
>> before_dec, after_dec = str(d).split('.')
>> float('.'.join((before_dec, after_dec[0:2])))
0.98
2018-01-03 edit
This answer isn't robust or mathematically correct. See Nilani Algiriyage's answer below for the correct way to do this using Decimal.quantize
method.