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	$27.89	5.742%	$29.4914	$29.49	$29.50	$29.50
Purchase #2	$159.78	8.537%	$173.4204	$173.42	$173.40	$173.40
Purchase #3	$94.51	10.830%	$104.7454	$104.75	$104.75	$104.70
Purchase #4	$109.81	9.712%	$120.4747	$120.47	$120.45	$120.50
Purchase #5	$47.65	11.463%	$53.1121	$53.11	$53.10	$53.10
Purchase #6	$152.86	3.293%	$157.8937	$157.89	$157.90	$157.90
Purchase #7	$153.27	4.191%	$159.6935	$159.69	$159.70	$159.70
7 purchase totals =	$745.77		$798.8312	$798.82	$798.80	$798.80