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	$71.38	11.678%	$79.7158	$79.72	$79.70	$79.70
Purchase #2	$29.26	9.312%	$31.9847	$31.98	$32.00	$32.00
Purchase #3	$188.54	11.200%	$209.6565	$209.66	$209.65	$209.70
Purchase #4	$95.48	5.294%	$100.5347	$100.53	$100.55	$100.50
Purchase #5	$40.81	5.196%	$42.9305	$42.93	$42.95	$42.90
Purchase #6	$138.78	6.707%	$148.088	$148.09	$148.10	$148.10
Purchase #7	$38.27	5.602%	$40.4139	$40.41	$40.40	$40.40
7 purchase totals =	$602.52		$653.3241	$653.32	$653.35	$653.30