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	$121.72	13.663%	$138.3506	$138.35	$138.35	$138.40
Purchase #2	$40.75	4.487%	$42.5785	$42.58	$42.60	$42.60
Purchase #3	$108.76	4.435%	$113.5835	$113.58	$113.60	$113.60
Purchase #4	$60.80	3.439%	$62.8909	$62.89	$62.90	$62.90
Purchase #5	$88.94	8.781%	$96.7498	$96.75	$96.75	$96.70
Purchase #6	$190.53	4.863%	$199.7955	$199.80	$199.80	$199.80
Purchase #7	$37.52	12.182%	$42.0907	$42.09	$42.10	$42.10
7 purchase totals =	$649.02		$696.0395	$696.04	$696.10	$696.10