The principal objective of a progressive or graduated sales tax is encourage wiser use of economic resources, which are becoming scarcer as world demand increases.
For example, auto prices of $20k, 40k, 60k, etc. would have progressively higher sales tax rates. Those with the means can choose to buy the more expensive vehicle with the higher sales tax rate, or something more economical. This would translate into capital investment flowing into more economical use of scarce resources.
And a progressive sales tax can be designed to lessen the burden on whatever group (poor, infirm, veteran, elderly) Congress in their "wisdom" deems appropriate.
In addition, necessities such as food & medical & education can be exempted or baselined.