Giving 15% to charity creates a Schedule A deduction against other taxable income. The reality is Romney paid less than 15% toward his taxable income because his charitable donations decreased his earned income tax rate. His charitable donations have been almost exclusively related to Mormonism. As he vowed when he went through the Mormon temple for the first time at aged 19, before his French mission, allegiance to Mormonism comes before ANYTHING else--under penalty of death. (That vow has since been altered in the temple ceremony but still holds true for Romney).