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	$183.99	6.599%	$196.1315	$196.13	$196.15	$196.10
Purchase #2	$17.41	8.509%	$18.8914	$18.89	$18.90	$18.90
Purchase #3	$14.30	10.798%	$15.8441	$15.84	$15.85	$15.80
Purchase #4	$35.89	8.557%	$38.9611	$38.96	$38.95	$39.00
Purchase #5	$69.60	11.703%	$77.7453	$77.75	$77.75	$77.70
Purchase #6	$123.39	11.734%	$137.8686	$137.87	$137.85	$137.90
Purchase #7	$22.77	9.169%	$24.8578	$24.86	$24.85	$24.90
7 purchase totals =	$467.35		$510.2998	$510.30	$510.30	$510.30