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	$9.95	6.338%	$10.5806	$10.58	$10.60	$10.60
Purchase #2	$134.32	11.646%	$149.9629	$149.96	$149.95	$150.00
Purchase #3	$128.94	10.793%	$142.8565	$142.86	$142.85	$142.90
Purchase #4	$66.76	10.759%	$73.9427	$73.94	$73.95	$73.90
Purchase #5	$104.72	12.247%	$117.5451	$117.55	$117.55	$117.50
Purchase #6	$107.71	3.734%	$111.7319	$111.73	$111.75	$111.70
Purchase #7	$42.46	10.241%	$46.8083	$46.81	$46.80	$46.80
7 purchase totals =	$594.86		$653.4280	$653.43	$653.45	$653.40