Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$144.79	13.416%	$164.215	$164.22	$164.20	$164.20
Purchase #2	$230.91	3.492%	$238.9734	$238.97	$238.95	$239.00
Purchase #3	$18.98	3.718%	$19.6857	$19.69	$19.70	$19.70
Purchase #4	$175.56	9.326%	$191.9327	$191.93	$191.95	$191.90
Purchase #5	$123.65	10.439%	$136.5578	$136.56	$136.55	$136.60
Purchase #6	$71.58	9.842%	$78.6249	$78.62	$78.60	$78.60
Purchase #7	$94.95	8.711%	$103.2211	$103.22	$103.20	$103.20
7 purchase totals =	$860.42		$933.2106	$933.21	$933.15	$933.20