Generally speaking the tax burden on the poor is very low. In many cases many poor people's effective total tax rate (including income, sales, property and any other types of taxes) is below zero.
It might appear that way, but consider the tax burden built into the goods and services they consume.
Even after accounting for sales tax many people have a negative tax rate. If you are talking about the taxes that corporations pay on their income, then this should really not be counted as the corporations still have more money then they otherwise would if they did not earn the money they earned.