Trading means little, just add up your deposits and withdrawals see which is bigger and report the difference, that's your profit or loss.
Remember unless it's a deposit or a withdrawal, then you haven't actually made a trade, it's all within the virtual world of the exchange and what you think you have done isn't real until you withdraw it.
This is really bad advice. Capital gains taxes are calculated based on your annual net trading gains (in addition to investments you may have liquidated during the tax year). You think stock traders can avoid paying taxes just by leaving gains in their E-trade account rather than withdrawing it? To the IRS, every transaction is potentially taxable. Withdrawals are not taxable.
In these early days, since cryptocurrency exchanges/brokers are not providing tax documents, traders will probably be able to
get away with a lot. But that doesn't mean that taxes aren't technically due.
Will they provide a document stating my total gains or losses, or am I responsible for totaling these things up and reporting them? I did a lot of trading earlier in the year and I can't find a simple solution for totaling anything; almost looks like a nightmare.
Bittrex won't provide any tax document. You are responsible. They can provide an exportable list of all your trades. You are supposed to calculate the cost basis of your entries and exits in USD to determine the capital gains. Trading against bitcoin is a real bitch for calculating taxes. You might consider hiring a CPA to do your returns if you're making good money trading.