How to I figure when to charge sales tax and how much?

I operate an eCommerce shopping cart site.  I am located in Kansas.  The products I sell are drop shipped directly to the customer.  The warehouse that does the dropshipping is located in Maine.  They also have a warehouse in California.  I know that if I sell something to someone in Kansas, I have to charge them sales tax.  The dropshipper is saying that they must charge ME sales tax for any drop shipments to Maine OR California.

Can any one point me to some good resources to help me figure out what information is actually correct?  

My confusion is this... If I sell to someone in Kansas, how do I make sure I charge the correct amount of tax?... Different cities have different tax rates.

If they (the dropshipper) charges me sales tax for shipments to Maine and California, do I collect that tax from the customer and if so, do I pay the states the tax or is it the responsibility of the dropshipper?  I'm guessing that all I am doing is re-reimbursing myself for what I am charged and I do not actually have to file these taxes.

I know this is a confusing subject but Im just looking for resources and advice from EXPERIENCED ecommerce retailers.

thanks.