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	$16.92	6.457%	$18.0125	$18.01	$18.00	$18.00
Purchase #2	$7.85	9.164%	$8.5694	$8.57	$8.55	$8.60
Purchase #3	$51.78	7.216%	$55.5164	$55.52	$55.50	$55.50
Purchase #4	$88.91	7.504%	$95.5818	$95.58	$95.60	$95.60
Purchase #5	$118.48	11.726%	$132.373	$132.37	$132.35	$132.40
Purchase #6	$204.56	11.248%	$227.5689	$227.57	$227.55	$227.60
Purchase #7	$96.76	3.807%	$100.4437	$100.44	$100.45	$100.40
7 purchase totals =	$585.26		$638.0657	$638.06	$638.00	$638.10