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	$236.66	11.176%	$263.1091	$263.11	$263.10	$263.10
Purchase #2	$118.83	3.715%	$123.2445	$123.24	$123.25	$123.20
Purchase #3	$103.75	7.509%	$111.5406	$111.54	$111.55	$111.50
Purchase #4	$70.71	13.665%	$80.3725	$80.37	$80.35	$80.40
Purchase #5	$26.96	13.467%	$30.5907	$30.59	$30.60	$30.60
Purchase #6	$112.74	10.239%	$124.2834	$124.28	$124.30	$124.30
Purchase #7	$6.33	11.534%	$7.0601	$7.06	$7.05	$7.10
7 purchase totals =	$675.98		$740.2009	$740.19	$740.20	$740.20