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	$145.62	9.754%	$159.8238	$159.82	$159.80	$159.80
Purchase #2	$163.57	10.341%	$180.4848	$180.48	$180.50	$180.50
Purchase #3	$117.83	8.486%	$127.8291	$127.83	$127.85	$127.80
Purchase #4	$42.69	7.627%	$45.946	$45.95	$45.95	$45.90
Purchase #5	$44.26	3.851%	$45.9645	$45.96	$45.95	$46.00
Purchase #6	$94.97	8.119%	$102.6806	$102.68	$102.70	$102.70
Purchase #7	$162.85	8.583%	$176.8274	$176.83	$176.85	$176.80
7 purchase totals =	$771.79		$839.5562	$839.55	$839.60	$839.50