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	$21.88	12.338%	$24.5796	$24.58	$24.60	$24.60
Purchase #2	$166.32	10.163%	$183.2231	$183.22	$183.20	$183.20
Purchase #3	$81.71	10.545%	$90.3263	$90.33	$90.35	$90.30
Purchase #4	$177.28	3.330%	$183.1834	$183.18	$183.20	$183.20
Purchase #5	$146.64	6.333%	$155.9267	$155.93	$155.95	$155.90
Purchase #6	$99.29	12.153%	$111.3567	$111.36	$111.35	$111.40
Purchase #7	$125.45	5.871%	$132.8152	$132.82	$132.80	$132.80
7 purchase totals =	$818.57		$881.4110	$881.42	$881.45	$881.40