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	$244.25	5.669%	$258.0965	$258.10	$258.10	$258.10
Purchase #2	$84.39	13.509%	$95.7902	$95.79	$95.80	$95.80
Purchase #3	$136.48	7.442%	$146.6368	$146.64	$146.65	$146.60
Purchase #4	$166.72	7.453%	$179.1456	$179.15	$179.15	$179.10
Purchase #5	$45.95	5.285%	$48.3785	$48.38	$48.40	$48.40
Purchase #6	$52.67	13.378%	$59.7162	$59.72	$59.70	$59.70
Purchase #7	$95.86	9.341%	$104.8143	$104.81	$104.80	$104.80
7 purchase totals =	$826.32		$892.5781	$892.59	$892.60	$892.50