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	$27.48	3.172%	$28.3517	$28.35	$28.35	$28.40
Purchase #2	$46.48	5.252%	$48.9211	$48.92	$48.90	$48.90
Purchase #3	$91.36	10.137%	$100.6212	$100.62	$100.60	$100.60
Purchase #4	$108.94	13.370%	$123.5053	$123.51	$123.50	$123.50
Purchase #5	$69.75	4.556%	$72.9278	$72.93	$72.95	$72.90
Purchase #6	$137.45	6.643%	$146.5808	$146.58	$146.60	$146.60
Purchase #7	$62.66	9.221%	$68.4379	$68.44	$68.45	$68.40
7 purchase totals =	$544.12		$589.3458	$589.35	$589.35	$589.30