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	$79.63	12.756%	$89.7876	$89.79	$89.80	$89.80
Purchase #2	$99.81	3.690%	$103.493	$103.49	$103.50	$103.50
Purchase #3	$92.48	11.746%	$103.3427	$103.34	$103.35	$103.30
Purchase #4	$132.83	7.596%	$142.9198	$142.92	$142.90	$142.90
Purchase #5	$116.64	3.643%	$120.8892	$120.89	$120.90	$120.90
Purchase #6	$218.54	9.863%	$240.0946	$240.09	$240.10	$240.10
Purchase #7	$157.72	12.539%	$177.4965	$177.50	$177.50	$177.50
7 purchase totals =	$897.65		$978.0234	$978.02	$978.05	$978.00