To explain how to set it up, I'll give some examples.

First, here's the shipping I use:

US/Canada:  1-4 cards: $1,  5-20 cards:  $2,  21+ cards:  $.10 each.
Most other Countries: 1-4 cards: $1.50,  5-20 cards: $3, 21+ cards: $.15 each.

So.. to set up the shipping rules, I need to set up 3 sets. One for US, one for Canada, and One for everyone else.

Each set has 1-4 cards, 5-20 cards, and 21-1000000 cards.

1-4 cards is a flat fee of $1 (US/Canada) or $1.50 (no country = everyone else)
5-20 cards is a flat fee of $2/$3
21-1000000 cards is a Sum fee of $.10/$.15

Here's a pic of what I have:

If I wanted my shipping per auction instead of per card, I would have chosen auctions instead of qty units.

How it calculates:

1. Query for the country the buyer is in, if not found, query for blank country.
2. If entry is by qty, add up qty, if by auc, add up number of auctions (weight not implemented yet)
3. Locate the range we are in. If it is a flat rate range, return that value and end.
4. If it is a sum range, take the number of items into that range we are in times the incremental sum. Add that to the running total.
5. If we still have ranges below that, go to the next range down. If it's a flat rate, add to the running total and end.
6. If not a flat rate repeat the last 2 steps until you run out of ranges or hit a flat rate.