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	$59.91	6.230%	$63.6424	$63.64	$63.65	$63.60
Purchase #2	$144.93	12.409%	$162.9144	$162.91	$162.90	$162.90
Purchase #3	$32.43	10.720%	$35.9065	$35.91	$35.90	$35.90
Purchase #4	$72.32	6.559%	$77.0635	$77.06	$77.05	$77.10
Purchase #5	$92.65	7.431%	$99.5348	$99.53	$99.55	$99.50
Purchase #6	$63.39	13.566%	$71.9895	$71.99	$72.00	$72.00
Purchase #7	$199.93	13.851%	$227.6223	$227.62	$227.60	$227.60
7 purchase totals =	$665.56		$738.6734	$738.66	$738.65	$738.60