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	$52.37	13.732%	$59.5614	$59.56	$59.55	$59.60
Purchase #2	$107.53	6.779%	$114.8195	$114.82	$114.80	$114.80
Purchase #3	$102.86	11.429%	$114.6159	$114.62	$114.60	$114.60
Purchase #4	$212.86	4.137%	$221.666	$221.67	$221.65	$221.70
Purchase #5	$84.83	8.273%	$91.848	$91.85	$91.85	$91.80
Purchase #6	$52.85	3.404%	$54.649	$54.65	$54.65	$54.60
Purchase #7	$8.59	5.546%	$9.0664	$9.07	$9.05	$9.10
7 purchase totals =	$621.89		$666.2262	$666.24	$666.15	$666.20