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	$75.85	3.748%	$78.6929	$78.69	$78.70	$78.70
Purchase #2	$48.47	6.193%	$51.4717	$51.47	$51.45	$51.50
Purchase #3	$41.61	9.267%	$45.466	$45.47	$45.45	$45.50
Purchase #4	$49.91	8.723%	$54.2636	$54.26	$54.25	$54.30
Purchase #5	$97.55	8.694%	$106.031	$106.03	$106.05	$106.00
Purchase #6	$107.45	8.809%	$116.9153	$116.92	$116.90	$116.90
Purchase #7	$50.33	8.833%	$54.7756	$54.78	$54.80	$54.80
7 purchase totals =	$471.17		$507.6161	$507.62	$507.60	$507.70