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	$70.77	9.341%	$77.3806	$77.38	$77.40	$77.40
Purchase #2	$148.72	13.205%	$168.3585	$168.36	$168.35	$168.40
Purchase #3	$56.72	5.291%	$59.7211	$59.72	$59.70	$59.70
Purchase #4	$94.96	11.532%	$105.9108	$105.91	$105.90	$105.90
Purchase #5	$111.92	10.311%	$123.4601	$123.46	$123.45	$123.50
Purchase #6	$22.77	9.489%	$24.9306	$24.93	$24.95	$24.90
Purchase #7	$42.67	12.792%	$48.1283	$48.13	$48.15	$48.10
7 purchase totals =	$548.53		$607.8900	$607.89	$607.90	$607.90