I always include all because that was the price I was willing to pay for that object. For a hyperbole; when I buy something for 1 dollar but the shipping is 99 dollars, I don't think the object is worth 1 dollar but at least 100 to me to even think about buying it.
It only gets complicated when you buy multiple things at once, there I either split it evenly or weighted depending on why I got that mixed offer (like I bought it just because of a single item the rest was irrelevant etc.).