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	$45.57	10.284%	$50.2564	$50.26	$50.25	$50.30
Purchase #2	$221.95	4.179%	$231.2253	$231.23	$231.25	$231.20
Purchase #3	$83.89	8.695%	$91.1842	$91.18	$91.20	$91.20
Purchase #4	$59.43	11.473%	$66.2484	$66.25	$66.25	$66.20
Purchase #5	$107.47	10.140%	$118.3675	$118.37	$118.35	$118.40
Purchase #6	$97.98	13.108%	$110.8232	$110.82	$110.80	$110.80
Purchase #7	$49.78	11.396%	$55.4529	$55.45	$55.45	$55.50
7 purchase totals =	$666.07		$723.5579	$723.56	$723.55	$723.60