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	$38.28	7.138%	$41.0124	$41.01	$41.00	$41.00
Purchase #2	$248.57	5.158%	$261.3912	$261.39	$261.40	$261.40
Purchase #3	$135.34	13.798%	$154.0142	$154.01	$154.00	$154.00
Purchase #4	$19.93	9.522%	$21.8277	$21.83	$21.85	$21.80
Purchase #5	$179.79	3.198%	$185.5397	$185.54	$185.55	$185.50
Purchase #6	$225.97	5.523%	$238.4503	$238.45	$238.45	$238.50
Purchase #7	$27.45	7.804%	$29.5922	$29.59	$29.60	$29.60
7 purchase totals =	$875.33		$931.8277	$931.82	$931.85	$931.80