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	$41.86	8.580%	$45.4516	$45.45	$45.45	$45.50
Purchase #2	$110.87	5.263%	$116.7051	$116.71	$116.70	$116.70
Purchase #3	$113.48	8.589%	$123.2268	$123.23	$123.25	$123.20
Purchase #4	$21.66	13.210%	$24.5213	$24.52	$24.50	$24.50
Purchase #5	$139.69	12.348%	$156.9389	$156.94	$156.95	$156.90
Purchase #6	$141.79	13.756%	$161.2946	$161.29	$161.30	$161.30
Purchase #7	$59.71	5.323%	$62.8884	$62.89	$62.90	$62.90
7 purchase totals =	$629.06		$691.0267	$691.03	$691.05	$691.00