[ic] rounding customers total up as a contribution

[Glenn McCalley]

Hi list,

We are doing a store for a political campaign.  They want to offer, on the 
checkout page, the chance to round your total up to a next step with the 
additional money being a contribution.  For example:
"Your total is $22.50.  Would you like to add $2.50 as a contribution, 
bringing your total to $25.00?"... with a button to click which adds the 
cart item "Contribution" at $2.50 and re-calcs everything.

Of course if the total is $44.00 the prompt should be for $6.00 more to a 
total of $50.00.  A step table will have to be determined, but you get the 
idea.  Thousands of small contributions add up.

Anybody ever done anything like this?

Regards,
Glenn.