What if my business has multiple locations? Which location determines sales tax rate?

Dear Mam,

In this case you have to Form a TAX GROUP for your company dealing there trade in different location or countries in this TAX GROUP there will be a legal person to control the common transaction of the company and consolidate the all transaction related to VAT  and filing Return to the Government

Tax system all depends upon the local governance, in India now it is GST so you have check with the local system 

If it is under one commercial register, it shall be treated as a single company. Therefore, all the results of the internal branches shall be collected in one State in one place, except for those whose legal nature is different or outside the State.