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	$11.94	5.716%	$12.6225	$12.62	$12.60	$12.60
Purchase #2	$31.81	5.837%	$33.6667	$33.67	$33.65	$33.70
Purchase #3	$154.96	9.466%	$169.6285	$169.63	$169.65	$169.60
Purchase #4	$222.39	7.341%	$238.7156	$238.72	$238.70	$238.70
Purchase #5	$219.95	9.191%	$240.1656	$240.17	$240.15	$240.20
Purchase #6	$60.82	9.205%	$66.4185	$66.42	$66.40	$66.40
Purchase #7	$84.62	6.414%	$90.0475	$90.05	$90.05	$90.00
7 purchase totals =	$786.49		$851.2649	$851.28	$851.20	$851.20