I'm running version 18.104.22.168.r990
This bug was found by accident, but it could cause some issues for some... I placed an order myself and since I am in the state that I sell in, I was correctly charged sales tax. Just to experience a return from a customer's perspective, I requested a return on the order as a customer. Then, I issued myself a refund as admin, and I marked the order appropriately.
I noticed that overall sales figure for the store on the dashboard included the (now returned) sale in the total. Curiosity lead me to see the tax the problem. Even though I had refunded the entire sale, sales tax from the order was still reported in the sales tax report.
I solved the problem for my report to end up to be correct by deleting the order and the return completely, but if I wanted to keep a record of the sales/return activities, I would have inaccurate sales and tax reports. You can easily duplicate the problem. I hope you can fix it as well
Thanks for your attention!