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	$146.94	7.639%	$158.1647	$158.16	$158.15	$158.20
Purchase #2	$175.53	5.137%	$184.547	$184.55	$184.55	$184.50
Purchase #3	$162.45	6.861%	$173.5957	$173.60	$173.60	$173.60
Purchase #4	$11.64	10.759%	$12.8923	$12.89	$12.90	$12.90
Purchase #5	$24.95	8.862%	$27.1611	$27.16	$27.15	$27.20
Purchase #6	$127.67	7.399%	$137.1163	$137.12	$137.10	$137.10
Purchase #7	$37.80	3.816%	$39.2424	$39.24	$39.25	$39.20
7 purchase totals =	$686.98		$732.7195	$732.72	$732.70	$732.70