Let me provide a few information on how the sales tax center works.
At this time, the option to delete a sales tax is unavailable QuickBooks Online (QBO). However, you can change its status to inactive. From there, you'll no longer receive notifications about it. Here's how:
Go to Taxes from the left menu, select Sales Tax.
Click the Sales tax settings link.
From the Action column, click the Edit drop-down arrow.