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	$36.93	12.811%	$41.6611	$41.66	$41.65	$41.70
Purchase #2	$131.52	5.277%	$138.4603	$138.46	$138.45	$138.50
Purchase #3	$105.61	10.386%	$116.5787	$116.58	$116.60	$116.60
Purchase #4	$59.85	5.415%	$63.0909	$63.09	$63.10	$63.10
Purchase #5	$146.96	13.367%	$166.6041	$166.60	$166.60	$166.60
Purchase #6	$161.98	10.246%	$178.5765	$178.58	$178.60	$178.60
Purchase #7	$38.33	10.736%	$42.4451	$42.45	$42.45	$42.40
7 purchase totals =	$681.18		$747.4167	$747.42	$747.45	$747.50