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	$36.91	3.293%	$38.1254	$38.13	$38.15	$38.10
Purchase #2	$133.62	13.186%	$151.2391	$151.24	$151.25	$151.20
Purchase #3	$242.51	5.752%	$256.4592	$256.46	$256.45	$256.50
Purchase #4	$29.50	8.683%	$32.0615	$32.06	$32.05	$32.10
Purchase #5	$109.98	9.798%	$120.7558	$120.76	$120.75	$120.80
Purchase #6	$117.65	12.141%	$131.9339	$131.93	$131.95	$131.90
Purchase #7	$150.52	4.481%	$157.2648	$157.26	$157.25	$157.30
7 purchase totals =	$820.69		$887.8397	$887.84	$887.85	$887.90