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	$143.91	10.716%	$159.3314	$159.33	$159.35	$159.30
Purchase #2	$20.50	4.217%	$21.3645	$21.36	$21.35	$21.40
Purchase #3	$49.82	3.510%	$51.5687	$51.57	$51.55	$51.60
Purchase #4	$133.92	12.521%	$150.6881	$150.69	$150.70	$150.70
Purchase #5	$46.63	3.244%	$48.1427	$48.14	$48.15	$48.10
Purchase #6	$18.29	13.491%	$20.7575	$20.76	$20.75	$20.80
Purchase #7	$47.73	10.290%	$52.6414	$52.64	$52.65	$52.60
7 purchase totals =	$460.80		$504.4943	$504.49	$504.50	$504.50