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	$42.81	6.178%	$45.4548	$45.45	$45.45	$45.50
Purchase #2	$238.64	5.430%	$251.5982	$251.60	$251.60	$251.60
Purchase #3	$72.25	5.537%	$76.2505	$76.25	$76.25	$76.30
Purchase #4	$40.81	10.672%	$45.1652	$45.17	$45.15	$45.20
Purchase #5	$152.49	4.159%	$158.8321	$158.83	$158.85	$158.80
Purchase #6	$175.30	5.249%	$184.5015	$184.50	$184.50	$184.50
Purchase #7	$51.34	3.564%	$53.1698	$53.17	$53.15	$53.20
7 purchase totals =	$773.64		$814.9721	$814.97	$814.95	$815.10