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	$26.37	12.311%	$29.6164	$29.62	$29.60	$29.60
Purchase #2	$133.47	6.267%	$141.8346	$141.83	$141.85	$141.80
Purchase #3	$131.53	11.381%	$146.4994	$146.50	$146.50	$146.50
Purchase #4	$181.95	4.585%	$190.2924	$190.29	$190.30	$190.30
Purchase #5	$19.25	8.503%	$20.8868	$20.89	$20.90	$20.90
Purchase #6	$25.38	9.217%	$27.7193	$27.72	$27.70	$27.70
Purchase #7	$183.27	13.766%	$208.4989	$208.50	$208.50	$208.50
7 purchase totals =	$701.22		$765.3478	$765.35	$765.35	$765.30