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	$24.72	9.298%	$27.0185	$27.02	$27.00	$27.00
Purchase #2	$187.94	8.826%	$204.5276	$204.53	$204.55	$204.50
Purchase #3	$92.90	11.480%	$103.5649	$103.56	$103.55	$103.60
Purchase #4	$12.93	13.566%	$14.6841	$14.68	$14.70	$14.70
Purchase #5	$162.39	3.821%	$168.5949	$168.59	$168.60	$168.60
Purchase #6	$123.81	3.381%	$127.996	$128.00	$128.00	$128.00
Purchase #7	$78.45	6.437%	$83.4998	$83.50	$83.50	$83.50
7 purchase totals =	$683.14		$729.8858	$729.88	$729.90	$729.90