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	$63.85	5.587%	$67.4173	$67.42	$67.40	$67.40
Purchase #2	$39.40	11.856%	$44.0713	$44.07	$44.05	$44.10
Purchase #3	$150.43	5.477%	$158.6691	$158.67	$158.65	$158.70
Purchase #4	$145.43	6.283%	$154.5674	$154.57	$154.55	$154.60
Purchase #5	$98.87	12.838%	$111.5629	$111.56	$111.55	$111.60
Purchase #6	$223.81	12.820%	$252.5024	$252.50	$252.50	$252.50
Purchase #7	$81.89	12.136%	$91.8282	$91.83	$91.85	$91.80
7 purchase totals =	$803.68		$880.6186	$880.62	$880.55	$880.70