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	$17.94	11.806%	$20.058	$20.06	$20.05	$20.10
Purchase #2	$109.93	12.355%	$123.5119	$123.51	$123.50	$123.50
Purchase #3	$23.98	3.856%	$24.9047	$24.90	$24.90	$24.90
Purchase #4	$94.57	6.496%	$100.7133	$100.71	$100.70	$100.70
Purchase #5	$145.32	12.227%	$163.0883	$163.09	$163.10	$163.10
Purchase #6	$249.56	13.866%	$284.164	$284.16	$284.15	$284.20
Purchase #7	$38.71	10.208%	$42.6615	$42.66	$42.65	$42.70
7 purchase totals =	$680.01		$759.1017	$759.09	$759.05	$759.20