Sales tax is not regressive. The tax does not decrease as the amount subject to tax increases.
FAIL. Sales tax is regressive because as the ratio of income to purchases increases, the proportion taxed decreases. Think of it this way, a person making $200K/year uses the same amount of laundry detergent as a person making $50K/year, yet the person making $50K will pay a higher percentage of their income in tax purchasing that item.