It is probable that you must charge state sales tax on the entire price. However, you can probably be exempt from paying state sales tax on equipment that you purchase for resale. This is something you have to get from the state, then register a business account with amazon that is sales tax exempt.
Then of course you report your sales to the state and pay your sales tax to the state according to their rules, separate from income taxes.
Many states require you to charge state sales tax if you sell to an in-state customer even if you are out of state. Some states may require you to collect and pay sales tax if you have a physical in-state presence, but that is becoming more out dated. However, this is quire complicated and there are probably business consultants whose entire business is helping you keep track of your out of state sales and remitting the proper sales tax in each state with the correct reporting.
Medical devices may be exempt from sales tax in some states. This is something else that varies from state to state, and you may need help knowing what items are subject to tax or tax exempt in each state. You may be required to charge sales tax on your personal services as well, depending on the state and type of service.
Sales tax you pay is a deductible business expense on the business income tax return (if you include the sales tax in your gross receipts).
