Help in setting up Shipper and Rates as follows...

Thanks again for all the complex work on making the VM application! I have used the cart on multiple projects and now almost exclusively use it.

I need to setup the shipping to do the following:

1 item first class $1.73
2 items first class $2.41
3 items first class $3.09
4 Priority Mail Small Flat Rate Box: $4.95
5-6 First Class $6.69
7-12 Priority Mail Regular/Medium Flat Rate Box: $10.70

Based on quantity of each item, can I set up the shipper to do this? If so, how? I understand there must be a weight on each product. I have set that up, however I get multiple shipping options at checkout when I set these up individually. Naturally, a shopper would choose the least expensive shipping option - even if they are ordering 12 items... So, can the cart automatically adjust based on quantities of items, or can I set it up by weight to automatically charge per the list above?

Thanks very much in advance!

Brandon