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	$33.74	10.797%	$37.3829	$37.38	$37.40	$37.40
Purchase #2	$144.37	4.793%	$151.2897	$151.29	$151.30	$151.30
Purchase #3	$158.52	6.615%	$169.0061	$169.01	$169.00	$169.00
Purchase #4	$85.38	6.432%	$90.8716	$90.87	$90.85	$90.90
Purchase #5	$200.33	8.475%	$217.308	$217.31	$217.30	$217.30
Purchase #6	$34.53	3.149%	$35.6173	$35.62	$35.60	$35.60
Purchase #7	$35.81	9.429%	$39.1865	$39.19	$39.20	$39.20
7 purchase totals =	$692.68		$740.6621	$740.67	$740.65	$740.70