I think they include the GST in Toyota Islamabad Motor's bill, so the prices are more or less the same.
They have the option whether you want to purchase oil in can (4 litres) or whether you want the exact amount of oil via dispenser (3.6 litres). Since my car is still new, I dont need extra oil for topping up. The oil is the same whether you buy it in can or through dispenser. I have two oil cans with 0.5 litres oil .. practically useless. I checked with Toyota, They have asked me to bring the leftover oil on next service, and it will be adjusted.