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	$108.72	11.523%	$121.2478	$121.25	$121.25	$121.20
Purchase #2	$19.81	5.268%	$20.8536	$20.85	$20.85	$20.90
Purchase #3	$79.65	3.182%	$82.1845	$82.18	$82.20	$82.20
Purchase #4	$80.35	10.845%	$89.064	$89.06	$89.05	$89.10
Purchase #5	$151.32	4.664%	$158.3776	$158.38	$158.40	$158.40
Purchase #6	$80.30	5.639%	$84.8281	$84.83	$84.85	$84.80
Purchase #7	$155.65	7.431%	$167.2164	$167.22	$167.20	$167.20
7 purchase totals =	$675.80		$723.7720	$723.77	$723.80	$723.80