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	$241.74	12.376%	$271.6577	$271.66	$271.65	$271.70
Purchase #2	$174.72	12.145%	$195.9397	$195.94	$195.95	$195.90
Purchase #3	$117.75	12.691%	$132.6937	$132.69	$132.70	$132.70
Purchase #4	$94.48	6.418%	$100.5437	$100.54	$100.55	$100.50
Purchase #5	$76.46	4.791%	$80.1232	$80.12	$80.10	$80.10
Purchase #6	$186.64	9.759%	$204.8542	$204.85	$204.85	$204.90
Purchase #7	$142.64	11.127%	$158.5116	$158.51	$158.50	$158.50
7 purchase totals =	$1,034.43		$1,144.3238	$1,144.31	$1,144.30	$1,144.30