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	$9.81	7.223%	$10.5186	$10.52	$10.50	$10.50
Purchase #2	$240.95	3.866%	$250.2651	$250.27	$250.25	$250.30
Purchase #3	$117.75	12.107%	$132.006	$132.01	$132.00	$132.00
Purchase #4	$72.26	8.777%	$78.6023	$78.60	$78.60	$78.60
Purchase #5	$27.53	7.205%	$29.5135	$29.51	$29.50	$29.50
Purchase #6	$23.75	13.159%	$26.8753	$26.88	$26.90	$26.90
Purchase #7	$68.79	5.857%	$72.819	$72.82	$72.80	$72.80
7 purchase totals =	$560.84		$600.5998	$600.61	$600.55	$600.60