Exported NiceHash CSV files include an exchange rate and a fiat amount both rounded to 2 decimal places. Koinly ignores the reported exchange rate and uses the fiat value to calculate a new exchange rate which leads to significant errors for cost basis calculations when paying fees.
The hashpower mining fee in fiat only has one significant figure, compared to the 7 used for the reported exchange rate. This means that exchange rates calculated from NiceHash imports have a huge error attached to them for these small amounts (> 15% in a lot of cases).