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	$98.80	12.847%	$111.4928	$111.49	$111.50	$111.50
Purchase #2	$15.42	10.413%	$17.0257	$17.03	$17.05	$17.00
Purchase #3	$137.39	7.626%	$147.8674	$147.87	$147.85	$147.90
Purchase #4	$108.35	8.417%	$117.4698	$117.47	$117.45	$117.50
Purchase #5	$72.65	11.317%	$80.8718	$80.87	$80.85	$80.90
Purchase #6	$9.74	7.710%	$10.491	$10.49	$10.50	$10.50
Purchase #7	$228.50	6.158%	$242.571	$242.57	$242.55	$242.60
7 purchase totals =	$670.85		$727.7895	$727.79	$727.75	$727.90