we're still getting this issue on CiviCRM 7.7.29.
I can't see that this was resolved in the issue mentioned in the previous post.
We've just validated that in 2 separate systems.
Does anyone have an update?

UPDATE - actually looks like the previous post link was for the wrong issue - this is the correct one, which showsn astatus is Open:
https://issues.civicrm.org/jira/browse/CRM-21485?jql=text%20~%20%22renewal%20taxes%22

Got it working - follow the links on the issue, click files to see the required code to be added.  Sales Tax was added on a backend renewal after applying the code.