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	$93.99	12.199%	$105.4558	$105.46	$105.45	$105.50
Purchase #2	$123.27	9.241%	$134.6614	$134.66	$134.65	$134.70
Purchase #3	$21.69	12.164%	$24.3284	$24.33	$24.35	$24.30
Purchase #4	$66.58	8.665%	$72.3492	$72.35	$72.35	$72.30
Purchase #5	$128.55	8.166%	$139.0474	$139.05	$139.05	$139.00
Purchase #6	$16.99	13.832%	$19.3401	$19.34	$19.35	$19.30
Purchase #7	$162.32	3.868%	$168.5985	$168.60	$168.60	$168.60
7 purchase totals =	$613.39		$663.7808	$663.79	$663.80	$663.70