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	$93.99	6.814%	$100.3945	$100.39	$100.40	$100.40
Purchase #2	$35.96	13.661%	$40.8725	$40.87	$40.85	$40.90
Purchase #3	$65.63	9.106%	$71.6063	$71.61	$71.60	$71.60
Purchase #4	$87.52	5.499%	$92.3327	$92.33	$92.35	$92.30
Purchase #5	$191.98	4.579%	$200.7708	$200.77	$200.75	$200.80
Purchase #6	$74.93	4.696%	$78.4487	$78.45	$78.45	$78.40
Purchase #7	$138.43	5.491%	$146.0312	$146.03	$146.05	$146.00
7 purchase totals =	$688.44		$730.4567	$730.45	$730.45	$730.40