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	$240.28	12.373%	$270.0098	$270.01	$270.00	$270.00
Purchase #2	$70.37	3.520%	$72.847	$72.85	$72.85	$72.80
Purchase #3	$137.30	4.826%	$143.9261	$143.93	$143.95	$143.90
Purchase #4	$30.39	8.782%	$33.0588	$33.06	$33.05	$33.10
Purchase #5	$65.86	9.454%	$72.0864	$72.09	$72.10	$72.10
Purchase #6	$132.89	6.663%	$141.7445	$141.74	$141.75	$141.70
Purchase #7	$75.88	6.679%	$80.948	$80.95	$80.95	$80.90
7 purchase totals =	$752.97		$814.6206	$814.63	$814.65	$814.50