I saw on CNN this morning that Mormons who do not tithe are not "members in good standing" and cannot use the temple for things like baptisms and other sacraments. I don't know if this is true or not.
According to the IRS,
If you receive a benefit because of your contribution such as merchandise, tickets to a ball game or other goods and services, then you can deduct only the amount that exceeds the fair market value of the benefit received.
So if a tithe is in effect payment to use the temple (and gain eternal life - no small benefit!) then it doesn't seem like it meets the IRS requirements for a charitable contribution. Is anyone in a position to call this tax fraud and petition the IRS to disallow it as a deduction? I'd love to see Mr. Romney get an audit with a new tax bill and a penalty - for the last 7 years, or however far back the IRS can go.
Once again - I'm not a tax accountant or tax attorney, nor am I a Mormon, so I don't know any more about this than I heard on CNN.
BTW - in my church, only the financial secretary knows who gives what. It makes no difference to anyone else. All the benefits of membership are freely available to all without regard to their level of giving - and in fact, are mostly available to non-members as well. (Non members cannot vote in congregation "business" meetings - other than that, they can participate in everything else.)