I don't think services are taxable in most U.S. states. You're probably providing a service, not a good.

Worst case, tell your customers to provide reseller certificates so that they pay the tax 12-15 months later instead of today. Hopefully they'll make a return on the extra 5-10% of hashrate they can buy, you get 5-10% more revenue, and the sales tax owed is diluted 10% by inflation.

Personally my business model will not be to sell hashrate or mining contracts. I would set up a new corporation for the customer so the full tax benefits of depreciation pass through to them. That also gives them a powerful incentive to re-invest their profit into more shares, in order to keep Uncle Sam away. That's one way to retain customers without forcing them into 12+ month contracts.