Hopefully one of your American friends can answer that for you. Here in Canada you can own stock in an RRSP (Registered Retirement Savings Plan) which is not taxable income until you sell the stock and take the money out of your account. If you were to loose money, when you withdrew the money after selling the stock, you could claim it as a loss against your personal income tax. I hold my stock in a Canadian TFSA (Tax Free Savings Account) so I didn't get a tax benefit when I put the money into the TFSA like you would with an RRSP. I could sell my stock anytime, withdraw the money out of the TFSA and not pay any income tax on it if I made money, but nor can I claim a loss if I were to loose money.
Unless you are asking about the actual $100 itself you receive as onboard credit, in that case, no, I do not pay any sales, state, or Canadian provincial tax on that. $100 credit just shows up on our S&S. Again, is that because I am a Canadian citizen? Not sure.
Exotic Western Caribbean - Dream (B2B) - November, 2013 (Our Honeymoon)
Eastern Caribbean - Dream (B2B) - November, 2013 (Our Wedding)
Mexician Riviera - Spirit - November, 2011
Western Caribbean - Freedom - January, 2011
Southern Caribbean - Miracle - November, 2010
Western Caribbean - Liberty - November, 2008
Eastern Caribbean - Valor - October, 2006