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	$102.70	9.855%	$112.8211	$112.82	$112.80	$112.80
Purchase #2	$57.77	13.208%	$65.4003	$65.40	$65.40	$65.40
Purchase #3	$144.61	12.305%	$162.4043	$162.40	$162.40	$162.40
Purchase #4	$97.86	6.426%	$104.1485	$104.15	$104.15	$104.10
Purchase #5	$19.54	6.619%	$20.8334	$20.83	$20.85	$20.80
Purchase #6	$157.82	9.103%	$172.1864	$172.19	$172.20	$172.20
Purchase #7	$136.43	6.307%	$145.0346	$145.03	$145.05	$145.00
7 purchase totals =	$716.73		$782.8286	$782.82	$782.85	$782.70