How to report the tax if I trade BTC to LTC? Assume I traded 100 times between BTC and LTC and I earned $100 IF I sell all coins at market price.

However, I don't want to sell my coins yet. How I can report to the US tax?
The IRS treats digital currencies as capital assets and are therefore subject to capital gains taxes. Any disposition of these digital currencies, including trading and spending, is a tax event and capital gains must be calculated in USD. 


References:
https://en.bitcoin.it/wiki/Tax_compliance