In some online stores, the buyer first collects a cart of goods, and then a surcharge for delivery, taxes, and so on is added to this amount. Customers don’t really like this kind of approach, and some of them, after seeing the surcharges, may change their minds about making a purchase. For the client, it looks as if you are trying to impose some unjustified expenses on them.
Do not wait for the moment when the client collects a full cart of goods: immediately show the total amount that they will have to pay. This is also important so that they don’t have a feeling of disappointment when they were counting on one amount, and then you add shipping and taxes and another amount is obtained. Therefore, the sooner the client sees exactly how much they have to pay, the better.