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	$233.31	13.106%	$263.8876	$263.89	$263.90	$263.90
Purchase #2	$242.39	4.537%	$253.3872	$253.39	$253.40	$253.40
Purchase #3	$119.32	10.189%	$131.4775	$131.48	$131.50	$131.50
Purchase #4	$189.75	11.514%	$211.5978	$211.60	$211.60	$211.60
Purchase #5	$198.72	11.602%	$221.7755	$221.78	$221.80	$221.80
Purchase #6	$33.43	6.668%	$35.6591	$35.66	$35.65	$35.70
Purchase #7	$21.50	6.847%	$22.9721	$22.97	$22.95	$23.00
7 purchase totals =	$1,038.42		$1,140.7568	$1,140.77	$1,140.80	$1,140.90