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	$49.87	9.370%	$54.5428	$54.54	$54.55	$54.50
Purchase #2	$148.58	6.465%	$158.1857	$158.19	$158.20	$158.20
Purchase #3	$81.78	9.235%	$89.3324	$89.33	$89.35	$89.30
Purchase #4	$51.80	4.807%	$54.29	$54.29	$54.30	$54.30
Purchase #5	$185.42	11.590%	$206.9102	$206.91	$206.90	$206.90
Purchase #6	$137.90	3.748%	$143.0685	$143.07	$143.05	$143.10
Purchase #7	$34.35	12.149%	$38.5232	$38.52	$38.50	$38.50
7 purchase totals =	$689.70		$744.8528	$744.85	$744.85	$744.80