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	$40.42	6.564%	$43.0732	$43.07	$43.05	$43.10
Purchase #2	$26.56	7.114%	$28.4495	$28.45	$28.45	$28.40
Purchase #3	$43.66	3.142%	$45.0318	$45.03	$45.05	$45.00
Purchase #4	$153.86	10.379%	$169.8291	$169.83	$169.85	$169.80
Purchase #5	$33.84	5.604%	$35.7364	$35.74	$35.75	$35.70
Purchase #6	$249.53	12.129%	$279.7955	$279.80	$279.80	$279.80
Purchase #7	$37.75	12.793%	$42.5794	$42.58	$42.60	$42.60
7 purchase totals =	$585.62		$644.4949	$644.50	$644.55	$644.40