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	$169.62	12.178%	$190.2763	$190.28	$190.30	$190.30
Purchase #2	$103.70	7.102%	$111.0648	$111.06	$111.05	$111.10
Purchase #3	$115.51	9.790%	$126.8184	$126.82	$126.80	$126.80
Purchase #4	$244.46	12.565%	$275.1764	$275.18	$275.20	$275.20
Purchase #5	$100.65	6.256%	$106.9467	$106.95	$106.95	$106.90
Purchase #6	$126.29	6.250%	$134.1831	$134.18	$134.20	$134.20
Purchase #7	$40.42	11.717%	$45.156	$45.16	$45.15	$45.20
7 purchase totals =	$900.65		$989.6217	$989.63	$989.65	$989.70