buyers complex faq flat implement mix product products purchased rate selling shipping site store thank-you

I read the Flat Rate Shipping FAQ on the site but I need something a little more complex. Is it possible to have shipping set up as the following:

1 product purchased = $5 flat rate shipping
2 products purchased = $10 flat rate shipping
3 products purchased = $15 flat rate shipping
4 or more products purchased = $20 flat rate shipping

I'm also going to be selling 10+ products in my store so buyers can mix and match and it doesn't affect the shipping. Please let me know if this is possible and if so how you implement it. Thank you!