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	$64.75	9.481%	$70.8889	$70.89	$70.90	$70.90
Purchase #2	$92.28	8.331%	$99.9678	$99.97	$99.95	$100.00
Purchase #3	$9.67	8.290%	$10.4716	$10.47	$10.45	$10.50
Purchase #4	$49.80	3.465%	$51.5256	$51.53	$51.55	$51.50
Purchase #5	$185.40	8.153%	$200.5157	$200.52	$200.50	$200.50
Purchase #6	$121.72	9.151%	$132.8586	$132.86	$132.85	$132.90
Purchase #7	$74.85	4.268%	$78.0446	$78.04	$78.05	$78.00
7 purchase totals =	$598.47		$644.2728	$644.28	$644.25	$644.30