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	$94.26	6.719%	$100.5933	$100.59	$100.60	$100.60
Purchase #2	$241.82	3.857%	$251.147	$251.15	$251.15	$251.10
Purchase #3	$146.79	13.788%	$167.0294	$167.03	$167.05	$167.00
Purchase #4	$56.42	8.188%	$61.0397	$61.04	$61.05	$61.00
Purchase #5	$173.62	9.129%	$189.4698	$189.47	$189.45	$189.50
Purchase #6	$144.53	4.251%	$150.674	$150.67	$150.65	$150.70
Purchase #7	$106.98	4.244%	$111.5202	$111.52	$111.50	$111.50
7 purchase totals =	$964.42		$1,031.4734	$1,031.47	$1,031.45	$1,031.40