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	$103.85	12.267%	$116.5893	$116.59	$116.60	$116.60
Purchase #2	$66.93	7.714%	$72.093	$72.09	$72.10	$72.10
Purchase #3	$179.64	5.342%	$189.2364	$189.24	$189.25	$189.20
Purchase #4	$102.39	12.154%	$114.8345	$114.83	$114.85	$114.80
Purchase #5	$14.73	8.657%	$16.0052	$16.01	$16.00	$16.00
Purchase #6	$152.72	13.587%	$173.4701	$173.47	$173.45	$173.50
Purchase #7	$164.52	10.159%	$181.2336	$181.23	$181.25	$181.20
7 purchase totals =	$784.78		$863.4621	$863.46	$863.50	$863.40