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	$49.36	13.230%	$55.8903	$55.89	$55.90	$55.90
Purchase #2	$165.45	8.847%	$180.0874	$180.09	$180.10	$180.10
Purchase #3	$42.62	11.854%	$47.6722	$47.67	$47.65	$47.70
Purchase #4	$25.42	9.482%	$27.8303	$27.83	$27.85	$27.80
Purchase #5	$157.42	8.350%	$170.5646	$170.56	$170.55	$170.60
Purchase #6	$83.60	7.591%	$89.9461	$89.95	$89.95	$89.90
Purchase #7	$18.53	5.337%	$19.5189	$19.52	$19.50	$19.50
7 purchase totals =	$542.40		$591.5098	$591.51	$591.50	$591.50