Navigate to System > List > Stores
Select the pencil icon for any store
Turn on “Override Sales Tax Lookup”
Also, be sure to set a tax rate in the Sales Tax field
How to
Set a Static Tax Rate
Ignore the TaxJar service on a per-store basis.

Navigate to System > List > Stores
Select the pencil icon for any store
Turn on “Override Sales Tax Lookup”
Also, be sure to set a tax rate in the Sales Tax field