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	$186.93	12.122%	$209.5897	$209.59	$209.60	$209.60
Purchase #2	$19.42	11.533%	$21.6597	$21.66	$21.65	$21.70
Purchase #3	$143.27	9.310%	$156.6084	$156.61	$156.60	$156.60
Purchase #4	$100.83	11.368%	$112.2924	$112.29	$112.30	$112.30
Purchase #5	$62.94	6.711%	$67.1639	$67.16	$67.15	$67.20
Purchase #6	$32.25	10.103%	$35.5082	$35.51	$35.50	$35.50
Purchase #7	$231.39	11.357%	$257.669	$257.67	$257.65	$257.70
7 purchase totals =	$777.03		$860.4913	$860.49	$860.45	$860.60