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	$248.80	3.133%	$256.5949	$256.59	$256.60	$256.60
Purchase #2	$9.39	7.595%	$10.1032	$10.10	$10.10	$10.10
Purchase #3	$148.32	11.841%	$165.8826	$165.88	$165.90	$165.90
Purchase #4	$96.84	11.345%	$107.8265	$107.83	$107.85	$107.80
Purchase #5	$136.37	11.240%	$151.698	$151.70	$151.70	$151.70
Purchase #6	$123.98	6.373%	$131.8812	$131.88	$131.90	$131.90
Purchase #7	$235.72	9.382%	$257.8353	$257.84	$257.85	$257.80
7 purchase totals =	$999.42		$1,081.8217	$1,081.82	$1,081.90	$1,081.80