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	$125.87	13.692%	$143.1041	$143.10	$143.10	$143.10
Purchase #2	$139.83	3.344%	$144.5059	$144.51	$144.50	$144.50
Purchase #3	$222.32	7.423%	$238.8228	$238.82	$238.80	$238.80
Purchase #4	$13.95	5.818%	$14.7616	$14.76	$14.75	$14.80
Purchase #5	$202.69	13.113%	$229.2687	$229.27	$229.25	$229.30
Purchase #6	$67.81	10.187%	$74.7178	$74.72	$74.70	$74.70
Purchase #7	$74.93	10.649%	$82.9093	$82.91	$82.90	$82.90
7 purchase totals =	$847.40		$928.0902	$928.09	$928.00	$928.10