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	$108.40	7.491%	$116.5202	$116.52	$116.50	$116.50
Purchase #2	$175.76	11.852%	$196.5911	$196.59	$196.60	$196.60
Purchase #3	$88.32	5.279%	$92.9824	$92.98	$93.00	$93.00
Purchase #4	$57.29	4.431%	$59.8285	$59.83	$59.85	$59.80
Purchase #5	$57.42	8.186%	$62.1204	$62.12	$62.10	$62.10
Purchase #6	$121.48	8.481%	$131.7827	$131.78	$131.80	$131.80
Purchase #7	$45.27	8.474%	$49.1062	$49.11	$49.10	$49.10
7 purchase totals =	$653.94		$708.9315	$708.93	$708.95	$708.90