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	$195.55	13.768%	$222.4733	$222.47	$222.45	$222.50
Purchase #2	$179.50	5.791%	$189.8948	$189.89	$189.90	$189.90
Purchase #3	$49.32	13.286%	$55.8727	$55.87	$55.85	$55.90
Purchase #4	$18.49	11.277%	$20.5751	$20.58	$20.60	$20.60
Purchase #5	$47.27	3.637%	$48.9892	$48.99	$49.00	$49.00
Purchase #6	$97.38	10.414%	$107.5212	$107.52	$107.50	$107.50
Purchase #7	$141.29	8.674%	$153.5455	$153.55	$153.55	$153.50
7 purchase totals =	$728.80		$798.8718	$798.87	$798.85	$798.90