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	$35.90	12.548%	$40.4047	$40.40	$40.40	$40.40
Purchase #2	$9.89	9.166%	$10.7965	$10.80	$10.80	$10.80
Purchase #3	$157.38	7.257%	$168.8011	$168.80	$168.80	$168.80
Purchase #4	$22.81	13.109%	$25.8002	$25.80	$25.80	$25.80
Purchase #5	$18.45	7.538%	$19.8408	$19.84	$19.85	$19.80
Purchase #6	$107.46	6.602%	$114.5545	$114.55	$114.55	$114.60
Purchase #7	$93.80	7.517%	$100.8509	$100.85	$100.85	$100.90
7 purchase totals =	$445.69		$481.0487	$481.04	$481.05	$481.10