Origin + Location = Sales Tax Amount
Sales tax is determined based on where your order is being shipped from and where it's being delivered. For example, a package traveling from Hawaii to New York will have a different tax rate than a package making its way to Colorado from Ohio.
However, it's not as simple as 1 + 1 = 2. Each state also has individual counties, cities, and townships that mandate their own sales tax requirements. In other words, you might be shipping that package to Colorado, but the amount could be different if you're shipping to Adams County as opposed to Delta.
Long story short, the location where the item is being shipped from and the intended delivery address are what determine how much sales tax you'll be charged. Keep this in mind when you place an order.