fistful brings up a good point: time, services, & materials vs cold, hard, cash.
A Bible study last year hit on this pretty hard: the tithe is not about the money. We use money as a proxy because it is convenient for many. But, some sort of time/skill/material/service donation will also do the trick...in many cases is preferable due to fellowship opportunities, proselytizing opportunities, etc. Dollars are useful, but putting a face on the "donation" for others to see has a value beyond what dollars can buy.
'Cause it ain't about the money.
That said, I have always been a "Net After Caesar" rather than a "Gross" man. The NAC is augmented by service, time, materials, skills, etc: Board of Trustees, work around the church & school, donated materials, use of skills, & all the rest. If I counted it all up and applied a fair charge for my time/materials, I have little doubt I would hit 10% of gross.