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	$163.42	9.216%	$178.4808	$178.48	$178.50	$178.50
Purchase #2	$47.55	10.343%	$52.4681	$52.47	$52.45	$52.50
Purchase #3	$169.46	11.528%	$188.9953	$189.00	$189.00	$189.00
Purchase #4	$53.98	6.578%	$57.5308	$57.53	$57.55	$57.50
Purchase #5	$89.99	10.782%	$99.6927	$99.69	$99.70	$99.70
Purchase #6	$124.57	12.189%	$139.7538	$139.75	$139.75	$139.80
Purchase #7	$12.76	4.341%	$13.3139	$13.31	$13.30	$13.30
7 purchase totals =	$661.73		$730.2354	$730.23	$730.25	$730.30