Conventions for monetary values

I'm curious if there are any prevailing conventions for representing a
monetary value in XML.

Currently, we use a complex type that includes a "unit" attribute whose
value is a 3 character ISO currency code, e.g.:

  <price unit="USD">10.00</price>

I've thought of changing this to use element content:
  <price>
    <unit>USD</unit>
    <value>10.00</value>
  </price>

I've seen some conventions that do this with a simple type, e.g.:
 
 <price>10.00 USD</price>

or worse:

 <price>10.00USD</price>   (note, no white space, so you can't define it as
a list type)

I'm not fond of these. I prefer leveraging the XML syntax to more explicitly
differentiate the number portion from the unit.

So what are other people doing? Are there any prevailing conventions out
there?