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	$18.92	5.188%	$19.9016	$19.90	$19.90	$19.90
Purchase #2	$133.47	11.563%	$148.9031	$148.90	$148.90	$148.90
Purchase #3	$199.25	5.569%	$210.3462	$210.35	$210.35	$210.30
Purchase #4	$100.51	10.523%	$111.0867	$111.09	$111.10	$111.10
Purchase #5	$16.72	9.663%	$18.3357	$18.34	$18.35	$18.30
Purchase #6	$49.66	6.216%	$52.7469	$52.75	$52.75	$52.70
Purchase #7	$89.97	13.509%	$102.124	$102.12	$102.10	$102.10
7 purchase totals =	$608.50		$663.4442	$663.45	$663.45	$663.30