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	$52.78	12.819%	$59.5459	$59.55	$59.55	$59.50
Purchase #2	$130.40	6.134%	$138.3987	$138.40	$138.40	$138.40
Purchase #3	$125.39	13.623%	$142.4719	$142.47	$142.45	$142.50
Purchase #4	$118.99	3.870%	$123.5949	$123.59	$123.60	$123.60
Purchase #5	$208.51	7.198%	$223.5185	$223.52	$223.50	$223.50
Purchase #6	$131.77	11.275%	$146.6271	$146.63	$146.65	$146.60
Purchase #7	$7.58	10.670%	$8.3888	$8.39	$8.40	$8.40
7 purchase totals =	$775.42		$842.5458	$842.55	$842.55	$842.50