Add task rate based on location and type of delivery when adding an item in the Sales Order Record

Client Script with entry point postSourcing can be used.

function postSourcing(scriptContext) {
           var currentRec = scriptContext.currentRecord;
           
           var type_of_delivery = currentRec.getValue({
                
                   fieldId: 'custbody_jj_type_of_delivery'
           })           

           if (type_of_delivery == 7 || type_of_delivery == 8) {
                var location_display = currentRec.getCurrentSublistText({
                   sublistId: 'item',
                   fieldId: 'location_display'
                });               

           var tax = salestaxSearch(location_display);                

           currentRec.setCurrentSublistText({
              sublistId: 'item',
              fieldId: 'taxrate1',
              text: tax,
              ignoreFieldChange: true
            });

}
function salestaxSearch(location_display) {
        
            var tax_rate;
            var salestaxitemSearchObj = search.create({
                type: "salestaxitem",
                filters:
                    [
                        ["city", "is", location_display]
                    ],
                columns:
                    [
                        search.createColumn({name: "rate", label: "Rate"})

                    ]
            });
            var searchResultCount = salestaxitemSearchObj.runPaged().count;
            
            salestaxitemSearchObj.run().each(function (result) {
                tax_rate = result.getValue(search.createColumn({name: "rate", label: "Rate"}))
            });

            return tax_rate;
        }