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	$79.43	12.758%	$89.5637	$89.56	$89.55	$89.60
Purchase #2	$140.98	12.577%	$158.7111	$158.71	$158.70	$158.70
Purchase #3	$69.86	5.706%	$73.8462	$73.85	$73.85	$73.80
Purchase #4	$58.83	9.795%	$64.5924	$64.59	$64.60	$64.60
Purchase #5	$155.27	13.478%	$176.1973	$176.20	$176.20	$176.20
Purchase #6	$211.49	5.407%	$222.9253	$222.93	$222.95	$222.90
Purchase #7	$106.73	12.246%	$119.8002	$119.80	$119.80	$119.80
7 purchase totals =	$822.59		$905.6362	$905.64	$905.65	$905.60