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	$200.25	7.598%	$215.465	$215.47	$215.45	$215.50
Purchase #2	$132.91	13.852%	$151.3207	$151.32	$151.30	$151.30
Purchase #3	$114.47	3.182%	$118.1124	$118.11	$118.10	$118.10
Purchase #4	$95.37	9.761%	$104.6791	$104.68	$104.70	$104.70
Purchase #5	$76.66	13.347%	$86.8918	$86.89	$86.90	$86.90
Purchase #6	$38.31	4.314%	$39.9627	$39.96	$39.95	$40.00
Purchase #7	$88.80	10.675%	$98.2794	$98.28	$98.30	$98.30
7 purchase totals =	$746.77		$814.7111	$814.71	$814.70	$814.80