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	$113.50	6.243%	$120.5858	$120.59	$120.60	$120.60
Purchase #2	$184.60	3.406%	$190.8875	$190.89	$190.90	$190.90
Purchase #3	$193.52	11.229%	$215.2504	$215.25	$215.25	$215.30
Purchase #4	$129.89	11.858%	$145.2924	$145.29	$145.30	$145.30
Purchase #5	$48.57	5.347%	$51.167	$51.17	$51.15	$51.20
Purchase #6	$94.90	10.831%	$105.1786	$105.18	$105.20	$105.20
Purchase #7	$38.70	8.359%	$41.9349	$41.93	$41.95	$41.90
7 purchase totals =	$803.68		$870.2966	$870.30	$870.35	$870.40