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	$200.99	8.126%	$217.3224	$217.32	$217.30	$217.30
Purchase #2	$233.51	3.426%	$241.5101	$241.51	$241.50	$241.50
Purchase #3	$131.69	10.589%	$145.6347	$145.63	$145.65	$145.60
Purchase #4	$37.57	5.859%	$39.7712	$39.77	$39.75	$39.80
Purchase #5	$195.96	11.443%	$218.3837	$218.38	$218.40	$218.40
Purchase #6	$44.88	4.580%	$46.9355	$46.94	$46.95	$46.90
Purchase #7	$37.93	12.595%	$42.7073	$42.71	$42.70	$42.70
7 purchase totals =	$882.53		$952.2649	$952.26	$952.25	$952.20