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	$210.62	13.584%	$239.2306	$239.23	$239.25	$239.20
Purchase #2	$78.86	13.185%	$89.2577	$89.26	$89.25	$89.30
Purchase #3	$116.94	13.305%	$132.4989	$132.50	$132.50	$132.50
Purchase #4	$11.75	5.764%	$12.4273	$12.43	$12.45	$12.40
Purchase #5	$83.34	11.245%	$92.7116	$92.71	$92.70	$92.70
Purchase #6	$215.38	6.736%	$229.888	$229.89	$229.90	$229.90
Purchase #7	$12.98	3.208%	$13.3964	$13.40	$13.40	$13.40
7 purchase totals =	$729.87		$809.4105	$809.42	$809.45	$809.40