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	$229.29	13.217%	$259.5953	$259.60	$259.60	$259.60
Purchase #2	$24.53	4.583%	$25.6542	$25.65	$25.65	$25.70
Purchase #3	$119.59	3.147%	$123.3535	$123.35	$123.35	$123.40
Purchase #4	$56.93	5.820%	$60.2433	$60.24	$60.25	$60.20
Purchase #5	$174.39	4.661%	$182.5183	$182.52	$182.50	$182.50
Purchase #6	$32.92	4.783%	$34.4946	$34.49	$34.50	$34.50
Purchase #7	$50.39	13.213%	$57.048	$57.05	$57.05	$57.00
7 purchase totals =	$688.04		$742.9072	$742.90	$742.90	$742.90