The entity that is charged the tax has nothing to do with who's actually paying the tax (in the real sense - the person who bears the burden of the tax). A sales tax that's added to a point-of-sales bill versus a sales tax that's invisible to the consumer and charged to the supplier has the exact same economic impact on both of them.

For example, FICA taxes are nominally paid 50% by the employer and 50% by the employee, but over 90% of the actual tax incidence falls on the employee. Even if we changed the law so that 100% of FICA taxes were paid for by the employer, employees' after-tax wages would be the same.

For the record I'm an LIC resident and generally opposed to Amazon under the proposed plan