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	$5.83	3.557%	$6.0374	$6.04	$6.05	$6.00
Purchase #2	$117.73	8.837%	$128.1338	$128.13	$128.15	$128.10
Purchase #3	$11.86	11.759%	$13.2546	$13.25	$13.25	$13.30
Purchase #4	$136.36	3.136%	$140.6362	$140.64	$140.65	$140.60
Purchase #5	$39.42	12.521%	$44.3558	$44.36	$44.35	$44.40
Purchase #6	$104.65	6.537%	$111.491	$111.49	$111.50	$111.50
Purchase #7	$228.75	5.334%	$240.9515	$240.95	$240.95	$241.00
7 purchase totals =	$644.60		$684.8603	$684.86	$684.90	$684.90