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	$134.45	13.621%	$152.7634	$152.76	$152.75	$152.80
Purchase #2	$19.55	10.168%	$21.5378	$21.54	$21.55	$21.50
Purchase #3	$224.36	10.247%	$247.3502	$247.35	$247.35	$247.40
Purchase #4	$62.75	3.636%	$65.0316	$65.03	$65.05	$65.00
Purchase #5	$98.38	13.557%	$111.7174	$111.72	$111.70	$111.70
Purchase #6	$52.59	4.197%	$54.7972	$54.80	$54.80	$54.80
Purchase #7	$63.90	11.465%	$71.2261	$71.23	$71.25	$71.20
7 purchase totals =	$655.98		$724.4237	$724.43	$724.45	$724.40