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	$88.98	13.302%	$100.8161	$100.82	$100.80	$100.80
Purchase #2	$72.73	8.193%	$78.6888	$78.69	$78.70	$78.70
Purchase #3	$143.69	5.667%	$151.8329	$151.83	$151.85	$151.80
Purchase #4	$245.47	12.190%	$275.3928	$275.39	$275.40	$275.40
Purchase #5	$58.74	13.624%	$66.7427	$66.74	$66.75	$66.70
Purchase #6	$224.45	5.361%	$236.4828	$236.48	$236.50	$236.50
Purchase #7	$19.26	3.117%	$19.8603	$19.86	$19.85	$19.90
7 purchase totals =	$853.32		$929.8164	$929.81	$929.85	$929.80