Apex Trigger :

trigger Quote_Trigger on Quote (before insert,before update) {
    if((Trigger.isInsert || Trigger.isUpdate) && Trigger.isBefore){
        QuoteTriggerHandler.handlebeforeInsert(Trigger.New);
    }
}

Trigger Helper class :

public class QuoteTriggerHandler{
    public static void handlebeforeInsert(List<Quote> listQuote){
        Map<String ,Id> salMap = new Map<String ,Id>();
        Set <String> city = new Set <String>();
        Set <String> state = new Set <String>();
        for(Quote quo : listQuote){
            city.add(quo.BillingCity);
        }
        for(Quote quo : listQuote){
            state.add(quo.BillingState);
        }
        List<Sales_Tax__c> saletax=  [select Id,City__c,State__c from Sales_Tax__c where  City__c IN:city AND State__c  IN:state];

        FOR(Sales_Tax__c SAL : saletax) {
            salMap.put(SAL.City__c+ '_' +SAL.State__c, SAL.Id);
        }
        for(Quote quo :listQuote) {

            if((quo.BillingCity != null ||quo.BillingCity != '') && (quo.BillingState != null || quo.BillingState !='')) {
                if(salMap.containsKey(quo.BillingCity+ '_' +quo.BillingState))
                    quo.SalesTax__c = salMap.get(quo.BillingCity+ '_' +quo.BillingState);
            }
        }


    }
}

Thanks
 Ajay