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	$65.51	12.133%	$73.4583	$73.46	$73.45	$73.50
Purchase #2	$178.78	12.124%	$200.4553	$200.46	$200.45	$200.50
Purchase #3	$125.52	9.832%	$137.8611	$137.86	$137.85	$137.90
Purchase #4	$186.42	11.874%	$208.5555	$208.56	$208.55	$208.60
Purchase #5	$104.25	7.195%	$111.7508	$111.75	$111.75	$111.80
Purchase #6	$101.43	6.632%	$108.1568	$108.16	$108.15	$108.20
Purchase #7	$136.68	8.563%	$148.3839	$148.38	$148.40	$148.40
7 purchase totals =	$898.59		$988.6217	$988.63	$988.60	$988.90