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	$231.52	10.293%	$255.3504	$255.35	$255.35	$255.40
Purchase #2	$96.43	7.311%	$103.48	$103.48	$103.50	$103.50
Purchase #3	$98.67	13.452%	$111.9431	$111.94	$111.95	$111.90
Purchase #4	$128.26	3.456%	$132.6927	$132.69	$132.70	$132.70
Purchase #5	$90.39	13.789%	$102.8539	$102.85	$102.85	$102.90
Purchase #6	$39.71	9.185%	$43.3574	$43.36	$43.35	$43.40
Purchase #7	$85.32	10.190%	$94.0141	$94.01	$94.00	$94.00
7 purchase totals =	$770.30		$843.6916	$843.68	$843.70	$843.80