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	$76.66	8.844%	$83.4398	$83.44	$83.45	$83.40
Purchase #2	$38.25	4.148%	$39.8366	$39.84	$39.85	$39.80
Purchase #3	$247.86	13.676%	$281.7573	$281.76	$281.75	$281.80
Purchase #4	$221.56	4.497%	$231.5236	$231.52	$231.50	$231.50
Purchase #5	$41.76	10.802%	$46.2709	$46.27	$46.25	$46.30
Purchase #6	$29.36	5.634%	$31.0141	$31.01	$31.00	$31.00
Purchase #7	$11.94	9.271%	$13.047	$13.05	$13.05	$13.00
7 purchase totals =	$667.39		$726.8893	$726.89	$726.85	$726.80