Taxation related to iexpenses

Hi,

Can anyone give me an overview/direction how tax is going to be calculated for iexpenses when it involves more then one country. I understand that we can assign tax code at the expense template level and in ebusiness tax we can define condition set to derive tax based on location. Now,

If an employee goes from CA to US. Some of the expenses will be related to CA and some related to US and he will submit all his expenses through his Canada iexpense responsibility. So, how the system is going to calculate US taxation for the US portion and CA taxes (HST) for the Canada portion. When both is club in one expense report, how can we have a differentiation logic. Any insight will be really helpful.