Rounding off in purchase invoice

As I am not registered for GST I constantly run into problems trying to get the purchase invoice totals to match.

Generally, the supplier will enter each unit price ex GST and the qty.
Each line will be totalled at the ex gst price
an ex gst total will be at the bottom of the invoice with a line below for the GST figure.
GST will be added as one figure (10% of the subtotal) to arrive at the invoice total.

As I don’t use GST in Manager, I have to enter each items value at the inc GST figure and have each line total be the total inc GST.

Rarely does my invoice total equal the suppliers invoice total and I spend many minutes tweeking figures here and there until I can get it to match. This often will involve changing multiple items pricing by small values. e.g. I may change a price of $191.565 to $191.56505 and this type of change may have to happen on multiple lines until I can get it to match.

This is VERY frustrating.

I would LOVE an easier, and quicker, solution to this issue.