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	$73.47	11.369%	$81.8228	$81.82	$81.80	$81.80
Purchase #2	$173.80	9.340%	$190.0329	$190.03	$190.05	$190.00
Purchase #3	$30.29	11.308%	$33.7152	$33.72	$33.70	$33.70
Purchase #4	$209.66	10.332%	$231.3221	$231.32	$231.30	$231.30
Purchase #5	$138.64	4.121%	$144.3534	$144.35	$144.35	$144.40
Purchase #6	$35.93	13.672%	$40.8423	$40.84	$40.85	$40.80
Purchase #7	$76.91	11.182%	$85.5101	$85.51	$85.50	$85.50
7 purchase totals =	$738.70		$807.5988	$807.59	$807.55	$807.50