Hey steve-allroadsin,
Mixing business and personal funds is never recommended, but sometimes it's necessary. It's vital to record taxes accurately to ensure your returns are all filed accurately. Sorting out sales tax is work best suited for an accountant. You can easily invite your accountant as a user to approach this together. To search for a pro in your area, simply head to the My Accountant tab in QuickBooks Online then click on Find a pro to help.
Let me know how this goes!