Australia Post Shipping application for Shopify replaces the shipping calculation done by Shopify. As such, you should make the delivery charge 0 inside Shopify Admin panel. The calculator will intelligently query Australia Post to get the real time quote and add a seperate shipping cost line to customer's cart.
This gives you an added benefit of clearly showing the total cost of the purchase before customers enter their full addresses. Customers can clearly see the total cost of the purchase. An informed customer is a customer who is likely to continue with the checkout process.
We also need the preference of a special product called Shipping be presented in your store. This product is added to the cart when shipping rate is estimated at the cart page. Due to restriction of Shopify, we cannot override the price of a product at the cart page so we made the price of the shipping product at one cent. For example, if the shipping rate is at 6.30, the shipping product is added to the cart at the price of 0.01 and quantity of 630. Total of the line is 6.30. To avoid confusion with customers, we have hidden the price and quantity of the shipping line in the cart. You will still see them when you examine your order. An example is attached. The The shipping method chosen by the customer is included as an extra description of the shipping line. The actual shipping method chose (Prepaid Parcel Post Plus..) is listed and the postcode customer entered (3000) is also listed. Note the shipping method Prepaid Parcel Post Plus 500g Satchel is the name of the service returned by Australia Post. You can provide your own description in the Shipping application like Regular Shipping (2-5 days)