GST applied on Bills- non percentage basis

GST applied on Bills- non percentage basis

Hi,
I sometimes receive bills which have multiple line items (100s of lines) and input GST is charged on various items at multiple rates (some items may be zero rated, others exempt and remaining standard rated). As it is not viable to enter all the line items of the bills and the applicable GST % on each line item, is there any way I can manually enter the non-percentage value of the GST as an aggregate total in the Bills Section?