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	$129.52	7.336%	$139.0216	$139.02	$139.00	$139.00
Purchase #2	$74.38	8.283%	$80.5409	$80.54	$80.55	$80.50
Purchase #3	$95.42	10.610%	$105.5441	$105.54	$105.55	$105.50
Purchase #4	$38.94	12.539%	$43.8227	$43.82	$43.80	$43.80
Purchase #5	$123.52	12.723%	$139.2354	$139.24	$139.25	$139.20
Purchase #6	$192.59	7.269%	$206.5894	$206.59	$206.60	$206.60
Purchase #7	$5.57	9.489%	$6.0985	$6.10	$6.10	$6.10
7 purchase totals =	$659.94		$720.8526	$720.85	$720.85	$720.70