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	$42.79	5.578%	$45.1768	$45.18	$45.20	$45.20
Purchase #2	$54.87	8.665%	$59.6245	$59.62	$59.60	$59.60
Purchase #3	$141.96	4.256%	$148.0018	$148.00	$148.00	$148.00
Purchase #4	$132.81	12.318%	$149.1695	$149.17	$149.15	$149.20
Purchase #5	$101.54	10.142%	$111.8382	$111.84	$111.85	$111.80
Purchase #6	$46.47	5.207%	$48.8897	$48.89	$48.90	$48.90
Purchase #7	$71.40	10.559%	$78.9391	$78.94	$78.95	$78.90
7 purchase totals =	$591.84		$641.6396	$641.64	$641.65	$641.60