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	$139.71	4.847%	$146.4817	$146.48	$146.50	$146.50
Purchase #2	$83.36	3.330%	$86.1359	$86.14	$86.15	$86.10
Purchase #3	$97.72	13.806%	$111.2112	$111.21	$111.20	$111.20
Purchase #4	$30.94	9.102%	$33.7562	$33.76	$33.75	$33.80
Purchase #5	$54.76	5.678%	$57.8693	$57.87	$57.85	$57.90
Purchase #6	$48.90	10.589%	$54.078	$54.08	$54.10	$54.10
Purchase #7	$38.48	5.492%	$40.5933	$40.59	$40.60	$40.60
7 purchase totals =	$493.87		$530.1256	$530.13	$530.15	$530.20