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	$179.95	6.602%	$191.8303	$191.83	$191.85	$191.80
Purchase #2	$123.58	11.401%	$137.6694	$137.67	$137.65	$137.70
Purchase #3	$54.57	7.717%	$58.7812	$58.78	$58.80	$58.80
Purchase #4	$152.59	13.180%	$172.7014	$172.70	$172.70	$172.70
Purchase #5	$146.43	4.509%	$153.0325	$153.03	$153.05	$153.00
Purchase #6	$167.89	6.804%	$179.3132	$179.31	$179.30	$179.30
Purchase #7	$71.58	6.574%	$76.2857	$76.29	$76.30	$76.30
7 purchase totals =	$896.59		$969.6137	$969.61	$969.65	$969.60