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	$112.63	13.274%	$127.5805	$127.58	$127.60	$127.60
Purchase #2	$92.93	12.415%	$104.4673	$104.47	$104.45	$104.50
Purchase #3	$114.72	11.491%	$127.9025	$127.90	$127.90	$127.90
Purchase #4	$71.91	8.774%	$78.2194	$78.22	$78.20	$78.20
Purchase #5	$68.85	8.732%	$74.862	$74.86	$74.85	$74.90
Purchase #6	$108.93	6.714%	$116.2436	$116.24	$116.25	$116.20
Purchase #7	$45.43	13.809%	$51.7034	$51.70	$51.70	$51.70
7 purchase totals =	$615.40		$680.9787	$680.97	$680.95	$681.00