Ability to divide shipping cost between products

Let's say I order 8 batteries at $10/each from my supplier and they charge $20 for shipping. When using Order Sync it will only state the cost of the item as $10 and the shipping fee isn't reflected - since the true cost of the batteries are $12.50/each. The shipping cost needs to be evenly divided among parts to get an accurate cost of goods sold. It could either be automatically divided by the amount of items in an order or I should be able to manually add the shipping cost to each item.