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	$247.58	4.315%	$258.2631	$258.26	$258.25	$258.30
Purchase #2	$173.46	12.314%	$194.8199	$194.82	$194.80	$194.80
Purchase #3	$149.64	13.123%	$169.2773	$169.28	$169.30	$169.30
Purchase #4	$122.65	9.111%	$133.8246	$133.82	$133.80	$133.80
Purchase #5	$136.87	11.685%	$152.8633	$152.86	$152.85	$152.90
Purchase #6	$62.72	8.850%	$68.2707	$68.27	$68.25	$68.30
Purchase #7	$139.80	13.654%	$158.8883	$158.89	$158.90	$158.90
7 purchase totals =	$1,032.72		$1,136.2072	$1,136.20	$1,136.15	$1,136.30