The price of this Bill differs slightly due to the price of each item is different. Now that I do I use the average of the total list price of the item.
The price of the bill is slightly different because of the price of each item is different. When I include the items I use an average of the prices of goods.
The price of both invoice is slightly different, because the price of each item is different. When I combine items I use the average price of the goods.