title: shopping cart observer
body: <p>I am trying to work something out in Magento, but I'm not sure what the best way of doing things are.</p>
  
  <p>I am selling fabric/material, which is expensive. I am therefore allowing customers to purchase 'samples' of these fabrics.</p>
  
  <p>What I need to do is:
  * Each of these samples are free ($00.00), but..
  * If the customer has 5 or more items (no more than 15 items) then I need to add a surcharge of $20 (to cover P&amp;P etc)</p>
  
  <p>So if a customer has added 8 samples to their cart, they need to be charged whatever they have in their cart currently, plus $20 for the samples.</p>
  
  <p>Could I do this in an observer method?</p>
  
  <p>Many thanks</p>