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	$163.92	4.252%	$170.8899	$170.89	$170.90	$170.90
Purchase #2	$244.31	5.184%	$256.975	$256.98	$257.00	$257.00
Purchase #3	$126.72	12.622%	$142.7146	$142.71	$142.70	$142.70
Purchase #4	$224.76	13.699%	$255.5499	$255.55	$255.55	$255.50
Purchase #5	$202.56	10.640%	$224.1124	$224.11	$224.10	$224.10
Purchase #6	$232.59	9.468%	$254.6116	$254.61	$254.60	$254.60
Purchase #7	$229.54	3.869%	$238.4209	$238.42	$238.40	$238.40
7 purchase totals =	$1,424.40		$1,543.2743	$1,543.27	$1,543.25	$1,543.20