On items purchased as "buy one get one free", can sales tax be charged on the "free" item?

This depends on the state you are in. Sometimes it means you get it free, i.e. no sales tax. Most times it means it is free and you pay the taxes, meaning they sell the item, charge the sales tax then deduct the cost of the second item. example...If you win a car you are responsible for the taxes. You may need to check the bottle cap product's website for verification.

Yep, you always pay sales tax and any CRV that is applicable to account for the item. The item is technically free but you still pay for the right of having it.

It depends on state law. In my state, California, sales tax is charged on the purchase price of the taxable items. In my Neighbor, Nevada, sales tax is charged on the actual marked price no matter if the customer uses a coupon.

Most states require that sales tax be collected in that situation, based on the current selling price of the item if you weren't getting the deal. The item was free. The tax is separate from the cost of the item.

Normally the items are rung up in the register. Taxes and everything applied then the cost of the second one is taken off.

Your bottle cap was the same as a manufacturer's coupon. In most states, the manufacturer's coupon is treated as a payment, the same as cash. However the coupon is only for the cost of the item, not the sales tax. You pay the sales tax. If you had a BOGO purchase where the promotion was done by the store, the store has not received payment for the item, so no sales tax should be charged.