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	$154.81	6.166%	$164.3556	$164.36	$164.35	$164.40
Purchase #2	$62.36	6.244%	$66.2538	$66.25	$66.25	$66.30
Purchase #3	$118.89	7.340%	$127.6165	$127.62	$127.60	$127.60
Purchase #4	$218.72	8.556%	$237.4337	$237.43	$237.45	$237.40
Purchase #5	$79.85	4.142%	$83.1574	$83.16	$83.15	$83.20
Purchase #6	$59.82	5.795%	$63.2866	$63.29	$63.30	$63.30
Purchase #7	$37.51	9.640%	$41.126	$41.13	$41.15	$41.10
7 purchase totals =	$731.96		$783.2296	$783.24	$783.25	$783.30