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	$154.29	4.285%	$160.9013	$160.90	$160.90	$160.90
Purchase #2	$63.95	12.146%	$71.7174	$71.72	$71.70	$71.70
Purchase #3	$132.77	3.649%	$137.6148	$137.61	$137.60	$137.60
Purchase #4	$5.81	9.790%	$6.3788	$6.38	$6.40	$6.40
Purchase #5	$94.70	11.476%	$105.5678	$105.57	$105.55	$105.60
Purchase #6	$64.69	8.445%	$70.1531	$70.15	$70.15	$70.20
Purchase #7	$29.87	8.825%	$32.506	$32.51	$32.50	$32.50
7 purchase totals =	$546.08		$584.8392	$584.84	$584.80	$584.90