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	$18.80	8.367%	$20.373	$20.37	$20.35	$20.40
Purchase #2	$10.38	3.640%	$10.7578	$10.76	$10.75	$10.80
Purchase #3	$59.77	10.725%	$66.1803	$66.18	$66.20	$66.20
Purchase #4	$116.36	6.197%	$123.5708	$123.57	$123.55	$123.60
Purchase #5	$80.41	8.492%	$87.2384	$87.24	$87.25	$87.20
Purchase #6	$150.82	4.397%	$157.4516	$157.45	$157.45	$157.50
Purchase #7	$108.36	3.160%	$111.7842	$111.78	$111.80	$111.80
7 purchase totals =	$544.90		$577.3561	$577.35	$577.35	$577.50