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	$51.77	4.778%	$54.2436	$54.24	$54.25	$54.20
Purchase #2	$100.25	4.351%	$104.6119	$104.61	$104.60	$104.60
Purchase #3	$73.83	10.239%	$81.3895	$81.39	$81.40	$81.40
Purchase #4	$199.87	8.294%	$216.4472	$216.45	$216.45	$216.40
Purchase #5	$121.80	4.240%	$126.9643	$126.96	$126.95	$127.00
Purchase #6	$156.37	10.222%	$172.3541	$172.35	$172.35	$172.40
Purchase #7	$202.41	11.588%	$225.8653	$225.87	$225.85	$225.90
7 purchase totals =	$906.30		$981.8759	$981.87	$981.85	$981.90