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	$9.55	11.461%	$10.6445	$10.64	$10.65	$10.60
Purchase #2	$216.59	10.126%	$238.5219	$238.52	$238.50	$238.50
Purchase #3	$80.95	11.711%	$90.4301	$90.43	$90.45	$90.40
Purchase #4	$207.72	13.413%	$235.5815	$235.58	$235.60	$235.60
Purchase #5	$22.51	13.559%	$25.5621	$25.56	$25.55	$25.60
Purchase #6	$154.69	10.290%	$170.6076	$170.61	$170.60	$170.60
Purchase #7	$199.82	4.181%	$208.1745	$208.17	$208.15	$208.20
7 purchase totals =	$891.83		$979.5222	$979.51	$979.50	$979.50