In my opinion, assuming a $10 per act statutory fee, the $100 would all be allocated to the ‘public officer fees’ and be thus exempt from S/E tax (Total fee, minus expenses, minus $100 [10 x $10]).
The total amount, less expense (Total fee, minus expenses).
Expenses can be captured on purchase (cartridges, paper, mileage, etc…) or on a unit cost (per page, per mile, etc…). I do the latter, averaging $0.027-$0.035 per page, recalculated periodically, factoring in all supplies. I also put a fixed ‘surcharge’ on each signing for folder, pens, masks, sanitizer, booties, etc.),
We have some good coverage of this issue at this NotaryCafe link.
Good luck,
HWB.