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	$188.43	6.263%	$200.2314	$200.23	$200.25	$200.20
Purchase #2	$60.26	10.264%	$66.4451	$66.45	$66.45	$66.40
Purchase #3	$44.61	8.456%	$48.3822	$48.38	$48.40	$48.40
Purchase #4	$101.60	4.214%	$105.8814	$105.88	$105.90	$105.90
Purchase #5	$144.81	12.605%	$163.0633	$163.06	$163.05	$163.10
Purchase #6	$119.31	3.308%	$123.2568	$123.26	$123.25	$123.30
Purchase #7	$135.99	4.767%	$142.4726	$142.47	$142.45	$142.50
7 purchase totals =	$795.01		$849.7328	$849.73	$849.75	$849.80