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	$36.87	9.366%	$40.3232	$40.32	$40.30	$40.30
Purchase #2	$151.38	7.422%	$162.6154	$162.62	$162.60	$162.60
Purchase #3	$50.50	9.535%	$55.3152	$55.32	$55.30	$55.30
Purchase #4	$40.81	12.301%	$45.83	$45.83	$45.85	$45.80
Purchase #5	$19.64	7.306%	$21.0749	$21.07	$21.05	$21.10
Purchase #6	$235.80	11.540%	$263.0113	$263.01	$263.00	$263.00
Purchase #7	$74.51	9.242%	$81.3962	$81.40	$81.40	$81.40
7 purchase totals =	$609.51		$669.5662	$669.57	$669.50	$669.50