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	$183.90	10.856%	$203.8642	$203.86	$203.85	$203.90
Purchase #2	$94.94	5.507%	$100.1683	$100.17	$100.15	$100.20
Purchase #3	$12.35	12.330%	$13.8728	$13.87	$13.85	$13.90
Purchase #4	$220.86	3.455%	$228.4907	$228.49	$228.50	$228.50
Purchase #5	$12.76	3.203%	$13.1687	$13.17	$13.15	$13.20
Purchase #6	$208.76	5.181%	$219.5759	$219.58	$219.60	$219.60
Purchase #7	$119.48	10.342%	$131.8366	$131.84	$131.85	$131.80
7 purchase totals =	$853.05		$910.9772	$910.98	$910.95	$911.10