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	$34.79	10.766%	$38.5355	$38.54	$38.55	$38.50
Purchase #2	$117.67	4.734%	$123.2405	$123.24	$123.25	$123.20
Purchase #3	$196.33	7.244%	$210.5521	$210.55	$210.55	$210.60
Purchase #4	$80.44	12.461%	$90.4636	$90.46	$90.45	$90.50
Purchase #5	$48.85	7.708%	$52.6154	$52.62	$52.60	$52.60
Purchase #6	$175.46	12.321%	$197.0784	$197.08	$197.10	$197.10
Purchase #7	$108.45	10.200%	$119.5119	$119.51	$119.50	$119.50
7 purchase totals =	$761.99		$831.9974	$832.00	$832.00	$832.00