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	$154.51	11.711%	$172.6047	$172.60	$172.60	$172.60
Purchase #2	$238.66	8.364%	$258.6215	$258.62	$258.60	$258.60
Purchase #3	$130.68	11.382%	$145.554	$145.55	$145.55	$145.60
Purchase #4	$46.88	3.240%	$48.3989	$48.40	$48.40	$48.40
Purchase #5	$25.74	7.620%	$27.7014	$27.70	$27.70	$27.70
Purchase #6	$213.59	4.850%	$223.9491	$223.95	$223.95	$223.90
Purchase #7	$20.73	5.413%	$21.8521	$21.85	$21.85	$21.90
7 purchase totals =	$830.79		$898.6817	$898.67	$898.65	$898.70