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	$41.83	6.307%	$44.4682	$44.47	$44.45	$44.50
Purchase #2	$141.64	5.159%	$148.9472	$148.95	$148.95	$148.90
Purchase #3	$10.27	8.163%	$11.1083	$11.11	$11.10	$11.10
Purchase #4	$78.30	13.462%	$88.8407	$88.84	$88.85	$88.80
Purchase #5	$184.79	8.560%	$200.608	$200.61	$200.60	$200.60
Purchase #6	$83.77	4.509%	$87.5472	$87.55	$87.55	$87.50
Purchase #7	$96.27	9.504%	$105.4195	$105.42	$105.40	$105.40
7 purchase totals =	$636.87		$686.9391	$686.95	$686.90	$686.80