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	$77.26	11.667%	$86.2739	$86.27	$86.25	$86.30
Purchase #2	$241.60	11.592%	$269.6063	$269.61	$269.60	$269.60
Purchase #3	$190.98	9.168%	$208.489	$208.49	$208.50	$208.50
Purchase #4	$127.25	13.135%	$143.9643	$143.96	$143.95	$144.00
Purchase #5	$225.75	9.777%	$247.8216	$247.82	$247.80	$247.80
Purchase #6	$32.47	10.282%	$35.8086	$35.81	$35.80	$35.80
Purchase #7	$14.99	6.241%	$15.9255	$15.93	$15.95	$15.90
7 purchase totals =	$910.30		$1,007.8892	$1,007.89	$1,007.85	$1,007.90