In order to prevent regressive tax on items purchased, many states make certain types of things non-taxable, especially food. (wiseGEEK)

A regressive tax system does not mean and likely would not result in low income earners paying more taxes than the wealthy, only that the effective tax rate relative to income or consumption would be a larger tax burden to low income earners. (Wikipedia)

This update explains that ballot initiatives to enact regressive tax policies died in Michigan and Montana, but survived to secure spots on the ballot in Arizona, Florida, Massachusetts and Oregon. (The Tax Justice Digest)