QB Issue Resolution:

Once you set up sales tax, you’ll need to make sure that the Tax box on the far right side of the Product/Service, has a check mark on it. In order for the sales tax to calculate. (Please see screenshot attached)

You might see this helpful article in applying sales tax rates to transactions: https://community.intuit.com/articles/1145198

Resolution for Issue 'Sales tax not calculating' available: Yes (Solved).
Source: Intuit Community forum.

Sales tax not calculating: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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