I have the same issue with Bittrex. Cannot figure out the numbers in the trade history.
I bought some CloakCoin today and in the "My Order History" table it shows as this

BID/ASK UNITS FILLED CLOAK UNITS TOTAL CLOAK ACTUAL RATE COST / PROCEEDS 0.00132105 13.15148308 13.15148308 0.00132104 -0.01741719

I did some maths as below:

UNITS FILLED * ACTUAL RATE = 0.017373635 - it's less than COST/PROCEEDS by 0.00004355

This difference  of 0.00004355 could be the fee of 0.25%  but the fee  

FEE counted as  UNITS FILLED * ACTUAL RATE * 0.25% = 0.000043434088 (rounded here to 12 decimals)

Total cost of the transaction including fee is like this :

UNITS FILLED * ACTUAL RATE + FEE = 0.017417069296 (rounded here to 12 decimals)

The difference between BITTREX's COST/PROCEEDS and my calculation of the cost of this transaction is

0.000000120704 BTC

This is a crazy small amount but the value of the transaction isn't big either.

Is BITTREX doing something doggy or I am missing something here?

NOTE
Rounding in the above calculation is only in the post. All calculation were done with actual figures