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	$70.38	10.833%	$78.0043	$78.00	$78.00	$78.00
Purchase #2	$90.42	10.514%	$99.9268	$99.93	$99.95	$99.90
Purchase #3	$138.60	3.775%	$143.8322	$143.83	$143.85	$143.80
Purchase #4	$138.36	3.350%	$142.9951	$143.00	$143.00	$143.00
Purchase #5	$59.81	6.605%	$63.7605	$63.76	$63.75	$63.80
Purchase #6	$246.66	4.176%	$256.9605	$256.96	$256.95	$257.00
Purchase #7	$82.58	8.675%	$89.7438	$89.74	$89.75	$89.70
7 purchase totals =	$826.81		$875.2232	$875.22	$875.25	$875.20