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	$40.78	7.352%	$43.7781	$43.78	$43.80	$43.80
Purchase #2	$24.29	12.717%	$27.379	$27.38	$27.40	$27.40
Purchase #3	$105.26	10.780%	$116.607	$116.61	$116.60	$116.60
Purchase #4	$171.42	4.379%	$178.9265	$178.93	$178.95	$178.90
Purchase #5	$79.99	11.870%	$89.4848	$89.48	$89.50	$89.50
Purchase #6	$215.96	8.622%	$234.5801	$234.58	$234.60	$234.60
Purchase #7	$20.46	6.390%	$21.7674	$21.77	$21.75	$21.80
7 purchase totals =	$658.16		$712.5229	$712.53	$712.60	$712.60