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	$104.56	6.732%	$111.599	$111.60	$111.60	$111.60
Purchase #2	$216.46	4.318%	$225.8067	$225.81	$225.80	$225.80
Purchase #3	$19.72	9.777%	$21.648	$21.65	$21.65	$21.60
Purchase #4	$246.69	5.744%	$260.8599	$260.86	$260.85	$260.90
Purchase #5	$123.47	10.322%	$136.2146	$136.21	$136.20	$136.20
Purchase #6	$7.61	3.763%	$7.8964	$7.90	$7.90	$7.90
Purchase #7	$165.89	10.847%	$183.8841	$183.88	$183.90	$183.90
7 purchase totals =	$884.40		$947.9087	$947.91	$947.90	$947.90