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	$138.89	6.831%	$148.3776	$148.38	$148.40	$148.40
Purchase #2	$11.97	13.794%	$13.6211	$13.62	$13.60	$13.60
Purchase #3	$228.95	13.132%	$259.0157	$259.02	$259.00	$259.00
Purchase #4	$111.65	10.527%	$123.4034	$123.40	$123.40	$123.40
Purchase #5	$128.76	8.276%	$139.4162	$139.42	$139.40	$139.40
Purchase #6	$18.82	10.778%	$20.8484	$20.85	$20.85	$20.80
Purchase #7	$135.93	4.221%	$141.6676	$141.67	$141.65	$141.70
7 purchase totals =	$774.97		$846.3500	$846.36	$846.30	$846.30