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	$113.37	12.692%	$127.7589	$127.76	$127.75	$127.80
Purchase #2	$35.32	13.772%	$40.1843	$40.18	$40.20	$40.20
Purchase #3	$127.47	13.412%	$144.5663	$144.57	$144.55	$144.60
Purchase #4	$31.62	12.114%	$35.4504	$35.45	$35.45	$35.50
Purchase #5	$52.94	6.645%	$56.4579	$56.46	$56.45	$56.50
Purchase #6	$13.53	3.448%	$13.9965	$14.00	$14.00	$14.00
Purchase #7	$241.49	12.544%	$271.7825	$271.78	$271.80	$271.80
7 purchase totals =	$615.74		$690.1968	$690.20	$690.20	$690.40