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	$79.53	4.624%	$83.2075	$83.21	$83.20	$83.20
Purchase #2	$87.61	9.291%	$95.7498	$95.75	$95.75	$95.70
Purchase #3	$104.38	7.520%	$112.2294	$112.23	$112.25	$112.20
Purchase #4	$113.87	8.511%	$123.5615	$123.56	$123.55	$123.60
Purchase #5	$106.57	4.580%	$111.4509	$111.45	$111.45	$111.50
Purchase #6	$152.99	5.161%	$160.8858	$160.89	$160.90	$160.90
Purchase #7	$160.90	13.679%	$182.9095	$182.91	$182.90	$182.90
7 purchase totals =	$805.85		$869.9944	$870.00	$870.00	$870.00