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	$132.57	8.516%	$143.8597	$143.86	$143.85	$143.90
Purchase #2	$55.85	6.713%	$59.5992	$59.60	$59.60	$59.60
Purchase #3	$159.60	12.341%	$179.2962	$179.30	$179.30	$179.30
Purchase #4	$47.25	5.649%	$49.9192	$49.92	$49.90	$49.90
Purchase #5	$193.58	10.299%	$213.5168	$213.52	$213.50	$213.50
Purchase #6	$124.76	13.677%	$141.8234	$141.82	$141.80	$141.80
Purchase #7	$40.26	5.269%	$42.3813	$42.38	$42.40	$42.40
7 purchase totals =	$753.87		$830.3958	$830.40	$830.35	$830.40