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	$26.29	4.273%	$27.4134	$27.41	$27.40	$27.40
Purchase #2	$245.39	6.167%	$260.5232	$260.52	$260.50	$260.50
Purchase #3	$244.35	12.739%	$275.4777	$275.48	$275.50	$275.50
Purchase #4	$157.32	9.767%	$172.6854	$172.69	$172.70	$172.70
Purchase #5	$77.72	9.676%	$85.2402	$85.24	$85.25	$85.20
Purchase #6	$10.73	11.269%	$11.9392	$11.94	$11.95	$11.90
Purchase #7	$70.90	12.125%	$79.4966	$79.50	$79.50	$79.50
7 purchase totals =	$832.70		$912.7757	$912.78	$912.80	$912.70