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When you are importing from Vietnam to the U.S.A, before your goods are released into the country, you will need to pay customs duties. On average, the customs tariff is around 3.5% and it’s among the lowest in the world.
The taxes that you will pay are calculated based on the CIF value of your goods.
Products that have a higher customs tariff are dairy products, sugars and confectionery, beverages and tobacco, clothing.
Non-agricultural goods such as machinery, autos and transportation equipment, information technology products, minerals and metals, petroleum, chemicals, textiles and clothing, leather and footwear, consumer goods, wood products, and fish and fish products, are subject to an industrial tariff levied either on an ad valorem basis (percentage of value) or on a specific basis (e.g., $1 per 100 pounds).

Each state has its own sales tax (it is varying from a state to another), there is no GST or VAT in the U.S.A. You will not have to pay the sales tax for an import of Vietnamese goods because it is only imposed on retail.
Also, the purchase of goods for reselling is exempted of sales tax.
Necessary products like machineries for agriculture, medicine, and so on, are generally exempted of sales tax in most of the states.

Become Familiar with Size and Weight Calculation Rules
If you want to transport goods via express delivery and air freight you should take into consideration these rules because the costs can be high – the actual weight is calculated in kilograms (kg), and the volume is calculated in cubic meters (CBM).

A) Calculating the actual weight – If the actual weight of the goods in kilograms is more significant than its dimensional weight, it will be calculated like this:
Actual weight of the package x cost per kilogram (this price varies from company to company).

B) When the volume of the goods is larger than the actual weight is called dimensional weight – this is an estimated weight calculated by multiplying the length of the package with the width and height divided by a dimensional factor, also called a DIM divisor. Dimensional factors are numbers set by the major freight carriers, and represent cubic inches per pound. The dimensional weight is the weight of the package at the minimum density accepted by the carrier.
International transport and logistics companies are based on the maximum value they can charge. For example, freight carriers like USPS, FedEx, or UPS calculate shipping charges based on whichever number is greater (actual weight or dimensional weight). For example, if you have a package that has the actual weight less than 31 kilograms (let’s say 29 kg), the freight carrier will charge for the dimensional weight of 31 kilograms since it is the greater number. For them, whichever number is higher becomes your billable weight.
Therefore, in some cases, to save money it is necessary to compress the package and reduce the measurement volume.
Finding an experienced freight forwarder will help you find the ideal solutions for shipping from Vietnam to the U.S.A, and will save you money and time.