Odoo will always automatically detect the FULL VALUE of the expense when using the OCR service. 

Taxes will not be itemized at the Expense level.

It is possible to have the full value split when the Journal Entries are automatically generated and posted.

First, create a purchase tax that is setup with the INCLUDED IN PRICE checkbox ON.  You will find this checkbox on the ADVANCED SETTINGS tab on the Tax.  Be sure to specify the account you want the tax to be expensed to on the DEFINITION tab.

Odoo will either detect the correct product (machine learning will try to match the NAME of the expense with the correct product - whether the expense is sent through the OCR service; whether the expense is emailed and the email subject contains the product name; or whether the expense is manually entered) or the user has the option to set the product when they enter or edit the Expense prior to submitting.

This means an expense like this:

Will be posted like this: