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	$137.86	12.869%	$155.6012	$155.60	$155.60	$155.60
Purchase #2	$103.41	4.278%	$107.8339	$107.83	$107.85	$107.80
Purchase #3	$235.92	5.795%	$249.5916	$249.59	$249.60	$249.60
Purchase #4	$153.80	12.340%	$172.7789	$172.78	$172.80	$172.80
Purchase #5	$215.69	10.516%	$238.372	$238.37	$238.35	$238.40
Purchase #6	$206.37	9.273%	$225.5067	$225.51	$225.50	$225.50
Purchase #7	$205.45	7.154%	$220.1479	$220.15	$220.15	$220.10
7 purchase totals =	$1,258.50		$1,369.8322	$1,369.83	$1,369.85	$1,369.80