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	$150.28	5.771%	$158.9527	$158.95	$158.95	$159.00
Purchase #2	$111.94	4.764%	$117.2728	$117.27	$117.25	$117.30
Purchase #3	$15.94	5.297%	$16.7843	$16.78	$16.80	$16.80
Purchase #4	$146.93	12.756%	$165.6724	$165.67	$165.65	$165.70
Purchase #5	$40.27	12.831%	$45.437	$45.44	$45.45	$45.40
Purchase #6	$222.57	5.458%	$234.7179	$234.72	$234.70	$234.70
Purchase #7	$91.67	9.228%	$100.1293	$100.13	$100.15	$100.10
7 purchase totals =	$779.60		$838.9664	$838.96	$838.95	$839.00