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	$60.39	10.704%	$66.8541	$66.85	$66.85	$66.90
Purchase #2	$46.43	4.367%	$48.4576	$48.46	$48.45	$48.50
Purchase #3	$169.87	6.461%	$180.8453	$180.85	$180.85	$180.80
Purchase #4	$14.43	3.343%	$14.9124	$14.91	$14.90	$14.90
Purchase #5	$93.56	8.349%	$101.3713	$101.37	$101.35	$101.40
Purchase #6	$99.58	11.771%	$111.3016	$111.30	$111.30	$111.30
Purchase #7	$124.84	13.848%	$142.1278	$142.13	$142.15	$142.10
7 purchase totals =	$609.10		$665.8701	$665.87	$665.85	$665.90