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	$89.47	11.338%	$99.6141	$99.61	$99.60	$99.60
Purchase #2	$142.80	8.187%	$154.491	$154.49	$154.50	$154.50
Purchase #3	$193.45	11.548%	$215.7896	$215.79	$215.80	$215.80
Purchase #4	$148.48	13.705%	$168.8292	$168.83	$168.85	$168.80
Purchase #5	$32.27	8.763%	$35.0978	$35.10	$35.10	$35.10
Purchase #6	$105.90	6.373%	$112.649	$112.65	$112.65	$112.60
Purchase #7	$245.52	13.592%	$278.8911	$278.89	$278.90	$278.90
7 purchase totals =	$957.89		$1,065.3618	$1,065.36	$1,065.40	$1,065.30