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	$86.82	8.629%	$94.3117	$94.31	$94.30	$94.30
Purchase #2	$105.40	10.708%	$116.6862	$116.69	$116.70	$116.70
Purchase #3	$111.57	11.409%	$124.299	$124.30	$124.30	$124.30
Purchase #4	$59.99	10.598%	$66.3477	$66.35	$66.35	$66.30
Purchase #5	$184.91	13.357%	$209.6084	$209.61	$209.60	$209.60
Purchase #6	$27.63	6.789%	$29.5058	$29.51	$29.50	$29.50
Purchase #7	$123.53	12.800%	$139.3418	$139.34	$139.35	$139.30
7 purchase totals =	$699.85		$780.1006	$780.11	$780.10	$780.00