Sales taxes are a form of regressive taxation. This is a fact.

Your definition of regressive is not quite accurate.

A regressive tax is a tax where people pay a larger percentage of their total income toward the tax as their total income decreases.

With sales taxes, even though the tax rate on purchases is the same for everyone, if poorer people spend a larger proportion of their income on these purchases, then the tax will be regressive.

Bridge and tunnel tolls are also regressive. If a person has to commute across a bridge, and pays $1 each way, at the end of the year, this will be a larger percentage of a poor person's income than of a rich person's.

On the issue of gasoline taxes alone, the NYTimes published a quite revealing map of the percentage of income spent on gas across the country.

You can see that in the incredibly-poor Mississippi River delta, the residents spend 16% of their total income on gasoline. In much of the northeast, the figure is under 5%. If you click back and forth between the 1st and 3rd tabs, the percentage of income spent on gasoline is almost a perfect correlation with total income. This shows that according to the definition, a tax that depends only on the amount of gasoline purchased is regressive.

I amend my answer, and believe that it can be done with one point. The plane would contain the point, and be perpendicular to the vector pointing from the origin to that point. Good puzzle, and deceptive!