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	$61.46	8.820%	$66.8808	$66.88	$66.90	$66.90
Purchase #2	$31.86	9.180%	$34.7847	$34.78	$34.80	$34.80
Purchase #3	$28.70	6.660%	$30.6114	$30.61	$30.60	$30.60
Purchase #4	$144.93	4.287%	$151.1431	$151.14	$151.15	$151.10
Purchase #5	$18.77	7.826%	$20.2389	$20.24	$20.25	$20.20
Purchase #6	$107.25	4.382%	$111.9497	$111.95	$111.95	$111.90
Purchase #7	$227.52	10.673%	$251.8032	$251.80	$251.80	$251.80
7 purchase totals =	$620.49		$667.4118	$667.40	$667.45	$667.30