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	$169.83	6.702%	$181.212	$181.21	$181.20	$181.20
Purchase #2	$136.67	5.273%	$143.8766	$143.88	$143.90	$143.90
Purchase #3	$142.82	4.537%	$149.2997	$149.30	$149.30	$149.30
Purchase #4	$97.71	10.823%	$108.2852	$108.29	$108.30	$108.30
Purchase #5	$77.55	7.606%	$83.4485	$83.45	$83.45	$83.40
Purchase #6	$186.83	7.167%	$200.2201	$200.22	$200.20	$200.20
Purchase #7	$101.62	10.468%	$112.2576	$112.26	$112.25	$112.30
7 purchase totals =	$913.03		$978.5997	$978.61	$978.60	$978.60