The poll tax was imposed on a per head basis, sometimes at differing amounts for different people, for those that wished to vote. The poll tax was considered very discriminatory, as it imposed higher taxes on certain groups of people. In addition, the wealthy often had an easy time affording the poll tax, whereas the poor were often unable to pay it all.
In the United States, the poll tax would be applied, even when individuals could not afford it. Those that were unable to pay the tax were often forced into hard labor to pay the tax. However, in locations where the poll tax is still in use, the rules which regulate the poll tax may differ and in most cases, it is simply imposed on a per head basis.
The Jim Crow laws which allowed for the poll tax, were implemented in the late nineteenth century. The creation of the poll tax may have been imposed in order to prevent non whites from voting, after they had just been granted the legal right to vote.
In addition, to make even it harder for non whites to vote, many states enacted an exemption to those that had voted previous to the law going into effect or those that had parents that voted previous to the law. In this way, only non whites and Native Americans were subjected to the poll tax, often making it impossible for them to vote.