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	$76.32	5.551%	$80.5565	$80.56	$80.55	$80.60
Purchase #2	$62.59	8.286%	$67.7762	$67.78	$67.80	$67.80
Purchase #3	$224.83	10.410%	$248.2348	$248.23	$248.25	$248.20
Purchase #4	$21.87	13.827%	$24.894	$24.89	$24.90	$24.90
Purchase #5	$103.98	5.168%	$109.3537	$109.35	$109.35	$109.40
Purchase #6	$227.43	12.729%	$256.3796	$256.38	$256.40	$256.40
Purchase #7	$107.45	4.246%	$112.0123	$112.01	$112.00	$112.00
7 purchase totals =	$824.47		$899.2071	$899.20	$899.25	$899.30