Many factors can change between the time you place an order and the time your order is shipped. Therefore, the amount appearing on your order as "Estimated Tax" may differ from the sales taxes ultimately charged.
How Sales Tax is Calculated
If an item is subject to sales or use tax in the state to which it is shipped, tax is generally calculated on its total selling price. In accordance with state tax laws, the total selling price of an item generally includes item-level shipping and handling charges, discounts and gift-wrap charges, and an allocation of order-level shipping and handling charges and discounts.
The tax rate applied to your order will generally be the combined state and local rate for the address where your order is approved or shipped. Therefore, the tax rate applied to your order may be different for an order shipped to your home address than it is for an order for the very same items shipped to your work address.