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	$35.91	12.206%	$40.2932	$40.29	$40.30	$40.30
Purchase #2	$63.83	6.827%	$68.1877	$68.19	$68.20	$68.20
Purchase #3	$130.44	9.545%	$142.8905	$142.89	$142.90	$142.90
Purchase #4	$105.82	7.568%	$113.8285	$113.83	$113.85	$113.80
Purchase #5	$30.71	12.393%	$34.5159	$34.52	$34.50	$34.50
Purchase #6	$128.60	12.364%	$144.5001	$144.50	$144.50	$144.50
Purchase #7	$27.64	3.688%	$28.6594	$28.66	$28.65	$28.70
7 purchase totals =	$522.95		$572.8753	$572.88	$572.90	$572.90