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	$249.83	3.182%	$257.7796	$257.78	$257.80	$257.80
Purchase #2	$200.46	8.528%	$217.5552	$217.56	$217.55	$217.60
Purchase #3	$222.28	11.198%	$247.1709	$247.17	$247.15	$247.20
Purchase #4	$221.25	5.592%	$233.6223	$233.62	$233.60	$233.60
Purchase #5	$233.47	11.285%	$259.8171	$259.82	$259.80	$259.80
Purchase #6	$48.64	10.410%	$53.7034	$53.70	$53.70	$53.70
Purchase #7	$100.55	11.186%	$111.7975	$111.80	$111.80	$111.80
7 purchase totals =	$1,276.48		$1,381.4460	$1,381.45	$1,381.40	$1,381.50