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	$160.75	6.497%	$171.1939	$171.19	$171.20	$171.20
Purchase #2	$150.47	4.311%	$156.9568	$156.96	$156.95	$157.00
Purchase #3	$110.49	11.528%	$123.2273	$123.23	$123.25	$123.20
Purchase #4	$216.77	9.280%	$236.8863	$236.89	$236.90	$236.90
Purchase #5	$100.64	12.223%	$112.9412	$112.94	$112.95	$112.90
Purchase #6	$123.32	13.729%	$140.2506	$140.25	$140.25	$140.30
Purchase #7	$21.93	6.567%	$23.3701	$23.37	$23.35	$23.40
7 purchase totals =	$884.37		$964.8262	$964.83	$964.85	$964.90