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	$143.25	10.797%	$158.7167	$158.72	$158.70	$158.70
Purchase #2	$105.56	8.246%	$114.2645	$114.26	$114.25	$114.30
Purchase #3	$88.92	11.366%	$99.0266	$99.03	$99.05	$99.00
Purchase #4	$223.49	6.859%	$238.8192	$238.82	$238.80	$238.80
Purchase #5	$99.70	13.614%	$113.2732	$113.27	$113.25	$113.30
Purchase #6	$36.67	10.678%	$40.5856	$40.59	$40.60	$40.60
Purchase #7	$133.66	8.170%	$144.58	$144.58	$144.60	$144.60
7 purchase totals =	$831.25		$909.2658	$909.27	$909.25	$909.30