shipping variables

Is there a way to adapt the shipping module so that I can provide 4 levels--

1-3 products: $8.25
4-5 products: $9.25
6-8 products: $10.50
9-12 products: $13.00

Otherwise, I will have to change to an entirely different shipping cart. There must be a way because I assume most people need more than a flat rate.
Please advise!!
Thanks.