I believe property taxes make up much of the school, etc. budgets in most states.
Sales tax might have once been a convenient way to tax people by locale, but it meshes poorly with the internet. If there must be a per-sale tax on internet goods, it should probably be a new type of tax which reflects the fact that the internet isn't related to geography. If anything, it should be a flat tax.
Sales tax is a flat tax within a state, but it's wildly variable from state to state - Delaware has none, Maryland has ~6%, NY has over 8%. I think a percentage agreed upon by all states is probably the agreement they mentioned, but I don't think they had enough detail to confirm it.