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	$170.86	5.811%	$180.7887	$180.79	$180.80	$180.80
Purchase #2	$216.58	13.840%	$246.5547	$246.55	$246.55	$246.60
Purchase #3	$10.92	11.382%	$12.1629	$12.16	$12.15	$12.20
Purchase #4	$158.61	4.256%	$165.3604	$165.36	$165.35	$165.40
Purchase #5	$130.79	10.796%	$144.9101	$144.91	$144.90	$144.90
Purchase #6	$52.25	4.714%	$54.7131	$54.71	$54.70	$54.70
Purchase #7	$35.85	8.485%	$38.8919	$38.89	$38.90	$38.90
7 purchase totals =	$775.86		$843.3818	$843.37	$843.35	$843.50