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	$58.31	3.130%	$60.1351	$60.14	$60.15	$60.10
Purchase #2	$57.52	4.289%	$59.987	$59.99	$60.00	$60.00
Purchase #3	$22.65	3.743%	$23.4978	$23.50	$23.50	$23.50
Purchase #4	$228.79	11.848%	$255.897	$255.90	$255.90	$255.90
Purchase #5	$24.82	3.186%	$25.6108	$25.61	$25.60	$25.60
Purchase #6	$105.61	5.394%	$111.3066	$111.31	$111.30	$111.30
Purchase #7	$50.35	5.123%	$52.9294	$52.93	$52.95	$52.90
7 purchase totals =	$548.05		$589.3637	$589.38	$589.40	$589.30