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	$177.96	6.442%	$189.4242	$189.42	$189.40	$189.40
Purchase #2	$229.69	11.248%	$255.5255	$255.53	$255.55	$255.50
Purchase #3	$39.56	12.793%	$44.6209	$44.62	$44.60	$44.60
Purchase #4	$64.50	11.575%	$71.9659	$71.97	$71.95	$72.00
Purchase #5	$234.85	9.246%	$256.5642	$256.56	$256.55	$256.60
Purchase #6	$140.69	7.472%	$151.2024	$151.20	$151.20	$151.20
Purchase #7	$10.78	7.776%	$11.6183	$11.62	$11.60	$11.60
7 purchase totals =	$898.03		$980.9214	$980.92	$980.85	$980.90