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	$122.69	8.868%	$133.5701	$133.57	$133.55	$133.60
Purchase #2	$32.98	7.656%	$35.5049	$35.50	$35.50	$35.50
Purchase #3	$30.61	9.126%	$33.4035	$33.40	$33.40	$33.40
Purchase #4	$217.45	10.180%	$239.5864	$239.59	$239.60	$239.60
Purchase #5	$6.56	4.187%	$6.8347	$6.83	$6.85	$6.80
Purchase #6	$48.72	11.802%	$54.4699	$54.47	$54.45	$54.50
Purchase #7	$47.54	13.708%	$54.0568	$54.06	$54.05	$54.10
7 purchase totals =	$506.55		$557.4263	$557.42	$557.40	$557.50