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	$18.94	12.572%	$21.3211	$21.32	$21.30	$21.30
Purchase #2	$96.33	4.260%	$100.4337	$100.43	$100.45	$100.40
Purchase #3	$121.90	3.471%	$126.1311	$126.13	$126.15	$126.10
Purchase #4	$230.85	10.763%	$255.6964	$255.70	$255.70	$255.70
Purchase #5	$168.81	10.230%	$186.0793	$186.08	$186.10	$186.10
Purchase #6	$90.26	11.866%	$100.9703	$100.97	$100.95	$101.00
Purchase #7	$132.40	13.561%	$150.3548	$150.35	$150.35	$150.40
7 purchase totals =	$859.49		$940.9867	$940.98	$941.00	$941.00