Romney Asked VP Shortlisters for Ten Years of Tax Returns – The Daily Beast
http://www.thedailybeast.com/articles/2012/09/13/romney-asked-vp-shortlisters-for-ten-years-of-tax-returns.html?taxes

As part of its vetting, the Romney campaign required at least some of the candidates on the short list—including the eventual winner of the GOP veepstakes, Ryan—to submit fully 10 years of tax returns, according to a knowledgeable source.

The requirement was consistent with the past practices of both Republican and Democratic campaigns. Indeed, in 2008, Mitt Romney turned over 23 years of taxes to John Mccain’s campaign when he was under consideration to be the Arizona senator’s running mate.