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	$235.60	8.334%	$255.2349	$255.23	$255.25	$255.20
Purchase #2	$44.61	7.797%	$48.0882	$48.09	$48.10	$48.10
Purchase #3	$241.57	11.577%	$269.5366	$269.54	$269.55	$269.50
Purchase #4	$110.40	6.432%	$117.5009	$117.50	$117.50	$117.50
Purchase #5	$20.89	6.129%	$22.1703	$22.17	$22.15	$22.20
Purchase #6	$28.86	13.335%	$32.7085	$32.71	$32.70	$32.70
Purchase #7	$49.43	10.553%	$54.6463	$54.65	$54.65	$54.60
7 purchase totals =	$731.36		$799.8857	$799.89	$799.90	$799.80