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	$78.90	7.259%	$84.6274	$84.63	$84.65	$84.60
Purchase #2	$143.70	11.845%	$160.7213	$160.72	$160.70	$160.70
Purchase #3	$49.94	8.333%	$54.1015	$54.10	$54.10	$54.10
Purchase #4	$52.31	3.123%	$53.9436	$53.94	$53.95	$53.90
Purchase #5	$21.31	3.717%	$22.1021	$22.10	$22.10	$22.10
Purchase #6	$57.94	13.192%	$65.5834	$65.58	$65.60	$65.60
Purchase #7	$72.37	9.365%	$79.1475	$79.15	$79.15	$79.10
7 purchase totals =	$476.47		$520.2268	$520.22	$520.25	$520.10