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	$46.45	4.415%	$48.5008	$48.50	$48.50	$48.50
Purchase #2	$76.61	13.478%	$86.9355	$86.94	$86.95	$86.90
Purchase #3	$41.51	9.327%	$45.3816	$45.38	$45.40	$45.40
Purchase #4	$29.85	11.413%	$33.2568	$33.26	$33.25	$33.30
Purchase #5	$11.56	6.183%	$12.2748	$12.27	$12.25	$12.30
Purchase #6	$79.95	10.718%	$88.519	$88.52	$88.50	$88.50
Purchase #7	$241.77	12.333%	$271.5875	$271.59	$271.60	$271.60
7 purchase totals =	$527.70		$586.4560	$586.46	$586.45	$586.50