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	$39.47	4.317%	$41.1739	$41.17	$41.15	$41.20
Purchase #2	$113.57	4.424%	$118.5943	$118.59	$118.60	$118.60
Purchase #3	$157.76	11.202%	$175.4323	$175.43	$175.45	$175.40
Purchase #4	$158.75	12.180%	$178.0858	$178.09	$178.10	$178.10
Purchase #5	$206.36	11.575%	$230.2462	$230.25	$230.25	$230.20
Purchase #6	$54.82	5.394%	$57.777	$57.78	$57.80	$57.80
Purchase #7	$79.70	12.378%	$89.5653	$89.57	$89.55	$89.60
7 purchase totals =	$810.43		$890.8748	$890.88	$890.90	$890.90