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	$162.79	9.491%	$178.2404	$178.24	$178.25	$178.20
Purchase #2	$148.91	4.693%	$155.8983	$155.90	$155.90	$155.90
Purchase #3	$160.79	10.490%	$177.6569	$177.66	$177.65	$177.70
Purchase #4	$199.43	11.709%	$222.7813	$222.78	$222.80	$222.80
Purchase #5	$130.66	3.777%	$135.595	$135.60	$135.60	$135.60
Purchase #6	$17.96	8.411%	$19.4706	$19.47	$19.45	$19.50
Purchase #7	$85.65	4.123%	$89.1813	$89.18	$89.20	$89.20
7 purchase totals =	$906.19		$978.8238	$978.83	$978.85	$978.90