Do you also believe that a person above your decided income level should be charged more for a good than a person who falls below it? For instance, if two people go into a restaurant and order the same meal, should the person, who makes $750,000 per year, be charged $50 for the meal as the person, who earns $735,000 per year, paying $15 for the same meal. Also, do you think that the person above the established income level should also have to pay a higher sales tax?
Also, what about the kid in college who has a job working at a clothing store part time, who may be getting more in salary and commission as opposed to his classmate who is working part time as a burger-flipper. The kid working in the clothing store can afford more than the burger flipper. Should he be taxed more?
A progressive sales tax is impracticable to administer. Where the brackets should be drawn, and what the rates should be, is a prudential matter, in part driven by spending and receipts. I suspect in your hypo, the two college kids would be in the same marginal income tax bracket, probably 10%. No, it is impracticable to have each bracket just one dollar wide, with the increase in rates for each dollar .0001% or whatever. Gee, I invoked practicality twice here. Maybe it might be catching.