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	$48.39	7.153%	$51.8513	$51.85	$51.85	$51.90
Purchase #2	$100.75	3.497%	$104.2732	$104.27	$104.25	$104.30
Purchase #3	$74.84	11.617%	$83.5342	$83.53	$83.55	$83.50
Purchase #4	$28.64	11.557%	$31.9499	$31.95	$31.95	$31.90
Purchase #5	$145.86	3.665%	$151.2058	$151.21	$151.20	$151.20
Purchase #6	$139.87	10.163%	$154.085	$154.09	$154.10	$154.10
Purchase #7	$87.31	9.397%	$95.5145	$95.51	$95.50	$95.50
7 purchase totals =	$625.66		$672.4139	$672.41	$672.40	$672.40