If you're Canadian, 100% back is not possible. Here's the CRA page with an example: https://www.canada.ca/en/revenue-agency/services/charities-g...

That's definitely not how it works in the US. Let's say you're in the 25% tax bracket. You have $100 in earnings. Normally, you would pay a $25 tax and have $75 left. If you donate that $100 to charity you simply don't have to pay the $25 tax. You're still out there $100.