Hello @111bruja888 thanks for your post and welcome to the Square Seller Community! You have two issues going on here, so lets address them one at a time...
the sales tax issue: this should automatically be added to your sales. You should setup your Sales Tax rate in your Square Dashboard. See this post about setting up a tax rate. Once you have your sales tax rate setup, you can turn it on/off for each item you sell, depending on if your State requires you to collect sales tax on that category of item.
As far as the processing fee...that cannot be set to automatically calculate the % for you. You can setup a service fee, but that would be a flat fee, or you'd have to manually calculate it. Be careful here though...there are some legal issues in passing on credit card processing fees to your customers. Please Google this issue, and search the forums here for other sellers who have asked the same question.
Credit card processing fees are generally seen as a cost of doing business, and you can deduct those as a valid biz expense on your taxes, thereby reducing your tax liability. It also keeps your customers happy because no shopper likes to pay additional fees for using their credit card. It's a win-win for biz and customers. I understand you see the fee as an extra charge that is costing you money, but there are costs associated with the moving of money between accounts (so the nominal processing fee covers that). If you want to avoid this all to together, you can create a CASH ONLY policy for your customers...but again, Customers don't like that usually. It's all about being super focused on your customer and proving a great shopping experience. Good luck to you, and I hope this helped to answer your question.
