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	$214.78	3.636%	$222.5894	$222.59	$222.60	$222.60
Purchase #2	$125.43	13.524%	$142.3932	$142.39	$142.40	$142.40
Purchase #3	$34.76	11.379%	$38.7153	$38.72	$38.70	$38.70
Purchase #4	$195.52	13.486%	$221.8878	$221.89	$221.90	$221.90
Purchase #5	$18.32	13.390%	$20.773	$20.77	$20.75	$20.80
Purchase #6	$8.53	3.264%	$8.8084	$8.81	$8.80	$8.80
Purchase #7	$6.64	5.211%	$6.986	$6.99	$7.00	$7.00
7 purchase totals =	$603.98		$662.1531	$662.16	$662.15	$662.20