It's not just a tax rate per address. It's per address per product. For example, in New York, clothing under $110 is exempt from state taxes but not necessarily exempt from county, city or other local taxes. Any clothing item over $110 is charged tax on the full price. In Massachusetts, clothing under $175 is exempt from state level sales tax but only the portion above $175 is taxed for higher ticket clothing items. In Connecticut only some clothing items under $50 are exempt from state sales tax. So, just in the category clothing, you can see that what is taxed, which portion is taxed and which items are included in the category definition is different. This is just on the state level and not including the myriad city, county, district and other taxes.
Taxes may be based on types of products: in Massachusetts, the American flag, among other items, is exempt from taxes; in Pennsylvania, textbooks and disposable diapers, among other items, are exempt; or as another poster mentioned, the Chicago Soft Drink Tax (where additional taxes are charged for "soft drinks".) Taxes may be based on areas: higher taxes for Bay Area Rapid Transit district and Louisiana tourism district or reduced taxes for New Jersey's Urban Enterprise Zones. Taxes can be charged based on intended use: in Indiana, a 15 ounce bag of potato chips is tax exempt (food items are exempt) whereas a personal sized bag is taxed because it is for immediate consumption and in California fertilizer is exempt if it's used to grow food.
Realistically, taxes can be based on any criteria that enters the twisted mind of a politician in the tiniest of jurisdictions, Currently, sales taxes can differ based upon temperature of food, whether the customer is a college student, distance from an airport, whether the product is in its original package, whether the product is intended to be used at home, etc. Most sales taxes are charged based upon the sales price while Hawaii also charges a portion of their excise tax (their sales tax equivalent) on the wholesale price and other states only charge on a portion of the sales price (such as the amount of clothing over $175 above.) Many states and municipalities also charge a restaurant and/or hotel tax and it's amazing what can get swept into that tax, such as candy, chips, soft drinks, juice boxes, bottled water, or other immediately consumable items, which an online retailer may sell.
In addition, many states have tax "holidays" when taxes are not charged: in Florida, a "back-to-school" tax holiday is often enacted on clothing, books and school supplies under a certain price; in Georgia, a tax Holiday, usually in October, is enacted on Energy Star rated appliances; Texas's tax holiday lasts for an entire weekend and applies to many items and exempts clothing and footwear under $100 but still taxes golf shoes, no matter the price.
Sales taxes are much more complicated than most people realize and they are completely at the whims of state, county, regional and municipal government officials. The category definitions are different from state to state and often different for local taxes within the state. This means the local taxes are often different from other locations within the state but also means that the local definition may differ from the state's own definitions. So for any given product, any of the taxes; state, county or municipal; may or may not apply. For a physical store, a local accountant can advise you how the taxes apply for that particular location but an online store would need to know what rate applies for every single product for every single address. Obviously, most of these combinations would never actually occur but the databases would need to contain a solution prior to the person placing the order.