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	$73.85	3.393%	$76.3557	$76.36	$76.35	$76.40
Purchase #2	$34.55	9.604%	$37.8682	$37.87	$37.85	$37.90
Purchase #3	$48.52	9.490%	$53.1245	$53.12	$53.10	$53.10
Purchase #4	$163.78	5.385%	$172.5996	$172.60	$172.60	$172.60
Purchase #5	$49.35	9.768%	$54.1705	$54.17	$54.15	$54.20
Purchase #6	$157.66	4.848%	$165.3034	$165.30	$165.30	$165.30
Purchase #7	$196.48	12.329%	$220.704	$220.70	$220.70	$220.70
7 purchase totals =	$724.19		$780.1259	$780.12	$780.05	$780.20