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	$91.64	8.600%	$99.521	$99.52	$99.50	$99.50
Purchase #2	$238.31	9.226%	$260.2965	$260.30	$260.30	$260.30
Purchase #3	$101.48	10.540%	$112.176	$112.18	$112.20	$112.20
Purchase #4	$10.29	8.690%	$11.1842	$11.18	$11.20	$11.20
Purchase #5	$202.76	9.660%	$222.3466	$222.35	$222.35	$222.30
Purchase #6	$95.56	10.672%	$105.7582	$105.76	$105.75	$105.80
Purchase #7	$54.76	3.125%	$56.4713	$56.47	$56.45	$56.50
7 purchase totals =	$794.80		$867.7538	$867.76	$867.75	$867.80