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	$38.43	4.456%	$40.1424	$40.14	$40.15	$40.10
Purchase #2	$103.54	4.677%	$108.3826	$108.38	$108.40	$108.40
Purchase #3	$108.77	6.769%	$116.1326	$116.13	$116.15	$116.10
Purchase #4	$123.90	6.439%	$131.8779	$131.88	$131.90	$131.90
Purchase #5	$181.53	4.761%	$190.1726	$190.17	$190.15	$190.20
Purchase #6	$42.68	13.513%	$48.4473	$48.45	$48.45	$48.40
Purchase #7	$141.60	10.484%	$156.4453	$156.45	$156.45	$156.40
7 purchase totals =	$740.45		$791.6007	$791.60	$791.65	$791.50