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	$51.47	10.159%	$56.6988	$56.70	$56.70	$56.70
Purchase #2	$151.88	5.787%	$160.6693	$160.67	$160.65	$160.70
Purchase #3	$120.31	9.161%	$131.3316	$131.33	$131.35	$131.30
Purchase #4	$49.83	9.700%	$54.6635	$54.66	$54.65	$54.70
Purchase #5	$208.88	4.184%	$217.6195	$217.62	$217.60	$217.60
Purchase #6	$231.43	5.468%	$244.0846	$244.08	$244.10	$244.10
Purchase #7	$105.69	5.726%	$111.7418	$111.74	$111.75	$111.70
7 purchase totals =	$919.49		$976.8091	$976.80	$976.80	$976.80