My business is headquartered in Illinois. I do not use the ATCS, but set up my amazon account to collect tax in Illinois. The tax is displayed and is included in my sales revenue, from Amazon. I am responsible for remitting the tax collected to Illinois, for Illinois sales. However, many states have enacted legislation and are going after Amazon (the deep pockets) to collect tax, for items sold online, to customers’ in their respective states. In these states, Amazon collects the tax (without you having to sign up for anything). The tax amount is displayed in your sales revenue summary, for each order, but you do not receive this tax income, from Amazon in their bi-weekly payouts (in my bookkeeping records, despite having the tax collection displayed in my order total, from Amazon, I do not record sales tax collected, as I did not collect it, nor receive it). Amazon remits to these tax entities on your behalf. Each year, more and more states enact legislation and Amazon does this, again, on your behalf. California seems to be the most aggressive, sending letters to individual sellers, trying to collect.
In your home state, if tax is not displayed in your orders, you have not collected it, but are responsible for it’s remittance. Some sellers, who have to follow Minimum Advertised Pricing (MAP), deliberately choose not to collect sales tax, within their tax area, to make their offer competitive with other sellers, in other states (that do not collect tax, in your home state), but these sellers still have to remit the sales tax owed, to their taxing entity. In your example, not seeing sales tax displayed, means you did not configure your account settings, to collect it, and that will have to come out of your bottom line.