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	$11.62	7.484%	$12.4896	$12.49	$12.50	$12.50
Purchase #2	$154.61	6.453%	$164.587	$164.59	$164.60	$164.60
Purchase #3	$52.48	8.840%	$57.1192	$57.12	$57.10	$57.10
Purchase #4	$198.52	11.680%	$221.7071	$221.71	$221.70	$221.70
Purchase #5	$134.91	12.423%	$151.6699	$151.67	$151.65	$151.70
Purchase #6	$210.88	3.621%	$218.516	$218.52	$218.50	$218.50
Purchase #7	$36.60	6.156%	$38.8531	$38.85	$38.85	$38.90
7 purchase totals =	$799.62		$864.9419	$864.95	$864.90	$865.00