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	$89.59	12.639%	$100.9133	$100.91	$100.90	$100.90
Purchase #2	$123.69	5.153%	$130.0637	$130.06	$130.05	$130.10
Purchase #3	$159.75	11.640%	$178.3449	$178.34	$178.35	$178.30
Purchase #4	$66.95	5.590%	$70.6925	$70.69	$70.70	$70.70
Purchase #5	$70.93	7.852%	$76.4994	$76.50	$76.50	$76.50
Purchase #6	$156.32	12.325%	$175.5864	$175.59	$175.60	$175.60
Purchase #7	$138.62	4.110%	$144.3173	$144.32	$144.30	$144.30
7 purchase totals =	$805.85		$876.4175	$876.41	$876.40	$876.40