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	$131.88	9.313%	$144.162	$144.16	$144.15	$144.20
Purchase #2	$150.54	10.113%	$165.7641	$165.76	$165.75	$165.80
Purchase #3	$59.71	4.827%	$62.5922	$62.59	$62.60	$62.60
Purchase #4	$158.42	3.377%	$163.7698	$163.77	$163.75	$163.80
Purchase #5	$65.95	9.743%	$72.3755	$72.38	$72.40	$72.40
Purchase #6	$14.90	10.488%	$16.4627	$16.46	$16.45	$16.50
Purchase #7	$137.53	4.655%	$143.932	$143.93	$143.95	$143.90
7 purchase totals =	$718.93		$769.0583	$769.05	$769.05	$769.20