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	$44.62	11.658%	$49.8218	$49.82	$49.80	$49.80
Purchase #2	$9.63	7.587%	$10.3606	$10.36	$10.35	$10.40
Purchase #3	$70.85	10.313%	$78.1568	$78.16	$78.15	$78.20
Purchase #4	$14.42	9.638%	$15.8098	$15.81	$15.80	$15.80
Purchase #5	$215.58	10.675%	$238.5932	$238.59	$238.60	$238.60
Purchase #6	$63.72	3.277%	$65.8081	$65.81	$65.80	$65.80
Purchase #7	$116.74	12.263%	$131.0558	$131.06	$131.05	$131.10
7 purchase totals =	$535.56		$589.6061	$589.61	$589.55	$589.70