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	$225.61	6.277%	$239.7715	$239.77	$239.75	$239.80
Purchase #2	$68.87	13.663%	$78.2797	$78.28	$78.30	$78.30
Purchase #3	$122.25	8.504%	$132.6461	$132.65	$132.65	$132.60
Purchase #4	$55.64	6.294%	$59.142	$59.14	$59.15	$59.10
Purchase #5	$24.30	6.553%	$25.8924	$25.89	$25.90	$25.90
Purchase #6	$83.82	13.625%	$95.2405	$95.24	$95.25	$95.20
Purchase #7	$100.89	10.536%	$111.5198	$111.52	$111.50	$111.50
7 purchase totals =	$681.38		$742.4920	$742.49	$742.50	$742.40