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	$37.68	6.581%	$40.1597	$40.16	$40.15	$40.20
Purchase #2	$57.90	9.865%	$63.6118	$63.61	$63.60	$63.60
Purchase #3	$44.89	4.247%	$46.7965	$46.80	$46.80	$46.80
Purchase #4	$39.42	3.591%	$40.8356	$40.84	$40.85	$40.80
Purchase #5	$60.89	9.206%	$66.4955	$66.50	$66.50	$66.50
Purchase #6	$115.81	9.508%	$126.8212	$126.82	$126.80	$126.80
Purchase #7	$218.46	3.521%	$226.152	$226.15	$226.15	$226.20
7 purchase totals =	$575.05		$610.8723	$610.88	$610.85	$610.90