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	$54.45	9.786%	$59.7785	$59.78	$59.80	$59.80
Purchase #2	$236.63	11.796%	$264.5429	$264.54	$264.55	$264.50
Purchase #3	$47.90	13.683%	$54.4542	$54.45	$54.45	$54.50
Purchase #4	$103.62	4.776%	$108.5689	$108.57	$108.55	$108.60
Purchase #5	$108.88	9.380%	$119.0929	$119.09	$119.10	$119.10
Purchase #6	$63.87	10.549%	$70.6076	$70.61	$70.60	$70.60
Purchase #7	$83.63	8.596%	$90.8188	$90.82	$90.80	$90.80
7 purchase totals =	$698.98		$767.8638	$767.86	$767.85	$767.90