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	$70.83	12.687%	$79.8162	$79.82	$79.80	$79.80
Purchase #2	$44.82	4.651%	$46.9046	$46.90	$46.90	$46.90
Purchase #3	$88.95	11.587%	$99.2566	$99.26	$99.25	$99.30
Purchase #4	$216.42	5.243%	$227.7669	$227.77	$227.75	$227.80
Purchase #5	$81.32	5.557%	$85.839	$85.84	$85.85	$85.80
Purchase #6	$199.69	10.404%	$220.4657	$220.47	$220.45	$220.50
Purchase #7	$112.32	9.527%	$123.0207	$123.02	$123.00	$123.00
7 purchase totals =	$814.35		$883.0697	$883.08	$883.00	$883.10