Hi ChrisW,
I keep track of all my trades with the data from DAS Trader after each day of trades. The same data is also available from IB. There is a difference due to the fact that DAS Trader doesn't calculate your exact fees. I use a proxy for these fees. I only use this tracking for trading assessment purposes.
For my taxes, IB makes tax slips available for each year. On these slips, you'll find the total sales and total cost. With this information, you can fill your taxes. I also keep track of my business spending (DAS memberships, electronic, etc.) in a Accounting ledger. This information is usefull at the end of the year for my taxes.
Hope this help,
Oli