You are not taxed for redeeming a gift card. You may only be liable for any gain on that asset or any income you receive from it.
If you receive a $100 gift card for Amazon and you end up selling it for $179 you will only be liable for the tax on the $79 gain ($179 - $100) when you sell it.
Please note that everyone's tax situation is different and we do not take into account your personal circumstances. For this reason, we suggest speaking to a tax professional regarding your own situation.