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	$104.52	11.627%	$116.6725	$116.67	$116.65	$116.70
Purchase #2	$79.79	7.569%	$85.8293	$85.83	$85.85	$85.80
Purchase #3	$166.94	10.274%	$184.0914	$184.09	$184.10	$184.10
Purchase #4	$151.43	5.849%	$160.2871	$160.29	$160.30	$160.30
Purchase #5	$125.27	5.600%	$132.2851	$132.29	$132.30	$132.30
Purchase #6	$55.50	13.134%	$62.7894	$62.79	$62.80	$62.80
Purchase #7	$215.51	3.365%	$222.7619	$222.76	$222.75	$222.80
7 purchase totals =	$898.96		$964.7167	$964.72	$964.75	$964.80