[ic] SalesTax multi by *billing* country?

[Interchange user]

Hey all,

I currently have SalesTax set to 'multi' with the appropriate tax categories 
set in the tax field of the country table, for the UK.

My question is: how can I calculate sales tax based on the billing country 
(if different to the shipping country), but still use the multi SalesTax type?

I searched the archives and found the following:


>> Well, I guess I mixed up what I was asking.  The technically correct way
>> to charge sales tax is the the purchaser, not necessarily the receiver.
>> So, if the billing state is filled in, then sales tax should be calculated
>> to this, if not, then assume that Billing Address == Shipping Address, so
>> calculate based on the Shipping State.
>>
>> Any ideas on how to implement this easily?
>
>
>In catalog.cfg:
>
>	SalesTax   tax_state
>
>At top of checkout.html and appropriate place in etc/profiles.order:
>
>	[if value b_state]
>		[value name=tax_state set="[value b_state]" hide=1]
>	[else]
>		[value name=tax_state set="[value state]" hide=1]
>	[/else]
>	[/if]


I was thinking about something like this, but how can I still use multiple 
tax categories? I'm guessing that I will need to set up a salestax.asc file, 
but I couldn't find any documentation explaining how to do this.

Any pointers?

Thank you.