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	$5.49	11.142%	$6.1017	$6.10	$6.10	$6.10
Purchase #2	$92.58	7.439%	$99.467	$99.47	$99.45	$99.50
Purchase #3	$239.77	3.141%	$247.3012	$247.30	$247.30	$247.30
Purchase #4	$116.70	11.796%	$130.4659	$130.47	$130.45	$130.50
Purchase #5	$39.90	4.181%	$41.5682	$41.57	$41.55	$41.60
Purchase #6	$239.70	7.451%	$257.56	$257.56	$257.55	$257.60
Purchase #7	$100.42	7.855%	$108.308	$108.31	$108.30	$108.30
7 purchase totals =	$834.56		$890.7720	$890.78	$890.70	$890.90