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