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	$43.70	5.262%	$45.9995	$46.00	$46.00	$46.00
Purchase #2	$46.31	8.770%	$50.3714	$50.37	$50.35	$50.40
Purchase #3	$243.78	5.554%	$257.3195	$257.32	$257.30	$257.30
Purchase #4	$37.41	9.320%	$40.8966	$40.90	$40.90	$40.90
Purchase #5	$227.71	12.204%	$255.4997	$255.50	$255.50	$255.50
Purchase #6	$132.66	7.256%	$142.2858	$142.29	$142.30	$142.30
Purchase #7	$102.32	5.828%	$108.2832	$108.28	$108.30	$108.30
7 purchase totals =	$833.89		$900.6557	$900.66	$900.65	$900.70