In DistributorCentral, sales tax is only applied to transactions between the distributor and the end customer. If sales tax is visible, you are viewing the customer-facing order, which reflects the tax calculated by TaxJar.
The purchase order (PO) sent to the supplier will not include sales tax, as it reflects the wholesale cost from the supplier.
For assistance with creating or editing a purchase order, please refer to the help guide: How to Create and Send Supplier Purchase Orders.