It sounds like you've never made a charitable donation under the American tax code. A dollar donated isn't a dollar saved. A dollar donated is (1-marginal tax rate) dollars saved.

You only deduct the percentage dictated by your tax bracket. So assuming he's in the 39.6% tax bracket his tax obligation is reduced by 39.6 cents for every dollar he donates.

This is an oversimplification, there's a bit more to it than that, but you get the point. Maybe.