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	$29.98	6.552%	$31.9443	$31.94	$31.95	$31.90
Purchase #2	$133.33	12.449%	$149.9283	$149.93	$149.95	$149.90
Purchase #3	$171.83	4.516%	$179.5898	$179.59	$179.60	$179.60
Purchase #4	$19.65	11.423%	$21.8946	$21.89	$21.90	$21.90
Purchase #5	$120.81	12.800%	$136.2737	$136.27	$136.25	$136.30
Purchase #6	$217.93	12.685%	$245.5744	$245.57	$245.55	$245.60
Purchase #7	$66.94	3.632%	$69.3713	$69.37	$69.35	$69.40
7 purchase totals =	$760.47		$834.5764	$834.56	$834.55	$834.60