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	$27.78	9.750%	$30.4886	$30.49	$30.50	$30.50
Purchase #2	$108.83	9.568%	$119.2429	$119.24	$119.25	$119.20
Purchase #3	$157.52	9.439%	$172.3883	$172.39	$172.40	$172.40
Purchase #4	$210.59	13.209%	$238.4068	$238.41	$238.40	$238.40
Purchase #5	$102.90	8.546%	$111.6938	$111.69	$111.70	$111.70
Purchase #6	$176.89	7.330%	$189.856	$189.86	$189.85	$189.90
Purchase #7	$155.48	13.234%	$176.0562	$176.06	$176.05	$176.10
7 purchase totals =	$939.99		$1,038.1326	$1,038.14	$1,038.15	$1,038.20