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	$14.83	12.766%	$16.7232	$16.72	$16.70	$16.70
Purchase #2	$103.97	4.404%	$108.5488	$108.55	$108.55	$108.50
Purchase #3	$199.40	11.417%	$222.1655	$222.17	$222.15	$222.20
Purchase #4	$67.99	9.807%	$74.6578	$74.66	$74.65	$74.70
Purchase #5	$189.66	8.585%	$205.9423	$205.94	$205.95	$205.90
Purchase #6	$157.79	6.397%	$167.8838	$167.88	$167.90	$167.90
Purchase #7	$233.64	13.655%	$265.5435	$265.54	$265.55	$265.50
7 purchase totals =	$967.28		$1,061.4649	$1,061.46	$1,061.45	$1,061.40