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	$47.59	7.455%	$51.1378	$51.14	$51.15	$51.10
Purchase #2	$53.99	9.811%	$59.287	$59.29	$59.30	$59.30
Purchase #3	$136.67	13.333%	$154.8922	$154.89	$154.90	$154.90
Purchase #4	$104.87	12.378%	$117.8508	$117.85	$117.85	$117.90
Purchase #5	$127.62	10.428%	$140.9282	$140.93	$140.95	$140.90
Purchase #6	$242.86	11.865%	$271.6753	$271.68	$271.70	$271.70
Purchase #7	$112.52	6.648%	$120.0003	$120.00	$120.00	$120.00
7 purchase totals =	$826.12		$915.7716	$915.78	$915.85	$915.80