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	$100.77	7.637%	$108.4658	$108.47	$108.45	$108.50
Purchase #2	$54.74	8.111%	$59.18	$59.18	$59.20	$59.20
Purchase #3	$156.47	8.785%	$170.2159	$170.22	$170.20	$170.20
Purchase #4	$134.77	11.178%	$149.8346	$149.83	$149.85	$149.80
Purchase #5	$47.60	5.242%	$50.0952	$50.10	$50.10	$50.10
Purchase #6	$59.51	3.143%	$61.3804	$61.38	$61.40	$61.40
Purchase #7	$10.39	11.427%	$11.5773	$11.58	$11.60	$11.60
7 purchase totals =	$564.25		$610.7492	$610.76	$610.80	$610.80