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	$92.38	9.117%	$100.8023	$100.80	$100.80	$100.80
Purchase #2	$130.81	13.590%	$148.5871	$148.59	$148.60	$148.60
Purchase #3	$207.84	6.545%	$221.4431	$221.44	$221.45	$221.40
Purchase #4	$51.34	6.347%	$54.5985	$54.60	$54.60	$54.60
Purchase #5	$103.57	7.564%	$111.404	$111.40	$111.40	$111.40
Purchase #6	$37.73	3.302%	$38.9758	$38.98	$39.00	$39.00
Purchase #7	$132.69	3.455%	$137.2744	$137.27	$137.25	$137.30
7 purchase totals =	$756.36		$813.0852	$813.08	$813.10	$813.10