If my employer doesn't have the GST rebate do I fill my employment expenses into the zero-rated fields or the GST taxable fields?

No, you would still enter your expenses based on what sales tax you paid. So if you paid GST, put the expense in the GST column.

To confirm, I put the full bill amount in the GST taxable column? Or is it only the portion of the bill before GST? 

You will put the full amount including the GST in the GST taxable column because you paid the GST on that expense.

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