This is really a question about who owns your product master data, and the real issue here is that "line" is not a drafting choice you get to make.
First, the Commission's own explanation counts by tariff classification, not by description and not by piece. Its example: several T-shirts are one charge, T-shirts plus a watch are two. So your mug set, tray and candle holders are as many charges as they have distinct classifications, and one mug is one. Declaring the whole box under a single description will not work if the codes differ; that is a misdeclaration waiting for an audit.
Second, the Commission says the seller or importer declares and pays. Who bears it commercially is your contract with the platform, not your customs paperwork, which is why you cannot tell from it.
Third, I am not sure about the handling fee and will not guess.
What you should have: one classification per SKU, held in one place, so the line count of any basket is computed before you quote a price, not discovered on an invoice.
Vivian, I sell very similar boxes out of Taipei (mugs, trays, the odd candle holder), so I went and read the Commission's page after Marcus's answer. The sentence that stuck is that it counts per item by tariff classification and not quantity, so five of the same mug is still one charge. That changed how I look at my bundles: a mug set plus a matching ceramic dish might be one line, while the bamboo tray is probably its own. I would rather find that out on a spreadsheet than on an invoice.
Do you already have a classification on every SKU, or is that the part you are still sorting out?
melody, honest answer: half. mugs and candle holders have codes, the bamboo stuff is a mess because my supplier gave me different ones for the same tray.
your bundle idea is the bit i hadnt thought about. i would want my forwarder to say yes in writing first.
did yours tell you how they count, or just "per line"?
Two codes for one tray: neither checked yet. Supplier's number is their export code, not your import one. Bring photo, material, use to a broker.