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	$72.52	11.268%	$80.6916	$80.69	$80.70	$80.70
Purchase #2	$41.94	10.580%	$46.3773	$46.38	$46.40	$46.40
Purchase #3	$10.41	9.748%	$11.4248	$11.42	$11.40	$11.40
Purchase #4	$128.36	7.735%	$138.2886	$138.29	$138.30	$138.30
Purchase #5	$38.70	5.512%	$40.8331	$40.83	$40.85	$40.80
Purchase #6	$87.55	13.539%	$99.4034	$99.40	$99.40	$99.40
Purchase #7	$75.97	9.527%	$83.2077	$83.21	$83.20	$83.20
7 purchase totals =	$455.45		$500.2265	$500.22	$500.25	$500.20