title: Free US sales-tax lookup (per zip etc.)?
body: <p>I am creating a pricing program. I need to calculate the amounts according to the current tax list in the US (in various places).</p>
  
  <p>I want to have a button 'Update taxes' in the administrative settings of the application, so when the user clicks it, it should download from somewhere the active tax amounts.</p>
  
  <p>So I actually want to have a function <code>decimal GetTax(string zip)</code>.</p>
  
  <p>Does anyone knows about a free downloadable xml, or RSS accessible or even a website that I can crawle in and get this info from?</p>