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	$12.33	9.447%	$13.4948	$13.49	$13.50	$13.50
Purchase #2	$93.46	6.540%	$99.5723	$99.57	$99.55	$99.60
Purchase #3	$144.61	4.291%	$150.8152	$150.82	$150.80	$150.80
Purchase #4	$13.70	4.422%	$14.3058	$14.31	$14.30	$14.30
Purchase #5	$220.82	12.233%	$247.8329	$247.83	$247.85	$247.80
Purchase #6	$234.92	8.800%	$255.593	$255.59	$255.60	$255.60
Purchase #7	$79.30	6.274%	$84.2753	$84.28	$84.30	$84.30
7 purchase totals =	$799.14		$865.8893	$865.89	$865.90	$865.90