Customs Fees From US To Canada

From what I understand, if the item is over $20, I would have to pay tax on the full value. Therefore if the value is $70 (what I paid), the tax would be 13% x 70 = $9.10. What is the remaining amount for?

Fortunately the new USMCA is bumping the exemption amount up to $150.

I live in Australia.

There was a period of decades, when I acquired coins from England. The business I was dealing with was a fully owned branch of an English company The coins were listed in England and were sent to Australia, where I examined them, before making an optional decision to buy.
British Value Added Tax (VAT) was not paid, because no purchase was made at that point. No Australian import taxes were paid, because the item was still fully owned by the company.
Transport Parcel fees were charged to me and added to my purchase price.

The coin pictured in my avatar was acquired in this way.
I have willed by collection to my kids. They won't be paying any taxes, save for auction fees. Australia doesn't charge death duties or estate taxes.

Not your fault Richard. At $20 Canada has one of the lowest exemption limits in the world. I'm used to receiving letter mail from the US rather than larger packages. It just caught me by surprise. The items I got from you are not sold in Canada. If I were to cross the border to buy the Dansco albums I would pay full retail plus state tax, then need to stay in the US for at least 24 hours or have to pay federal/provincial tax at the border on the way back in.