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	$131.94	3.496%	$136.5526	$136.55	$136.55	$136.60
Purchase #2	$105.33	6.210%	$111.871	$111.87	$111.85	$111.90
Purchase #3	$103.27	9.499%	$113.0796	$113.08	$113.10	$113.10
Purchase #4	$6.27	8.134%	$6.78	$6.78	$6.80	$6.80
Purchase #5	$183.30	6.693%	$195.5683	$195.57	$195.55	$195.60
Purchase #6	$50.97	7.615%	$54.8514	$54.85	$54.85	$54.90
Purchase #7	$48.81	9.762%	$53.5748	$53.57	$53.55	$53.60
7 purchase totals =	$629.89		$672.2777	$672.27	$672.25	$672.50