GST invoice heading

Hi, 

I deal with both taxable & exempted goods sales. I got doubt regarding the heading to be used for supply. 

For some customers I supply only taxable good, for some customers I supply only exempted goods. 
For some customers I supply both taxable & exempted goods.

Kindly update how invoice heading should be for each cases like tax invoice or bill of supply. And can i invoice both taxable & exempted supply in same invoice for registered customer