[Zope] Finagling Around Strange Zope Quirk

[Ben Ocean]

Hi;
I have a variable that is set thus:
<dtml-call "REQUEST.set('shipping',_.int(subtotal)*.05)">
and sent in a form thus:
<input type=hidden name=shipping value=<dtml-var shipping>>
where I would like it to be called thus:
<dtml-var shipping fmt=dollars-and-cents>
That doesn't work. I thought maybe it had been converted to a string, so I 
tried this:
<dtml-let shippingit="_.int(shipping)">
<dtml-var shippingit fmt=dollars-and-cents>
</dtml-let>
but that threw an error that it was already an integer and could not be 
converted. I give! How do I get this variable to render in 
dollars-and-cents? Can I convert the integer into a string and work that angle?
TIA,
BenO