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	$48.41	6.267%	$51.4439	$51.44	$51.45	$51.40
Purchase #2	$111.69	6.309%	$118.7365	$118.74	$118.75	$118.70
Purchase #3	$85.30	4.382%	$89.0378	$89.04	$89.05	$89.00
Purchase #4	$26.91	8.768%	$29.2695	$29.27	$29.25	$29.30
Purchase #5	$167.93	3.260%	$173.4045	$173.40	$173.40	$173.40
Purchase #6	$90.53	10.756%	$100.2674	$100.27	$100.25	$100.30
Purchase #7	$20.37	10.130%	$22.4335	$22.43	$22.45	$22.40
7 purchase totals =	$551.14		$584.5931	$584.59	$584.60	$584.50