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	$30.78	4.797%	$32.2565	$32.26	$32.25	$32.30
Purchase #2	$178.79	12.209%	$200.6185	$200.62	$200.60	$200.60
Purchase #3	$5.37	5.441%	$5.6622	$5.66	$5.65	$5.70
Purchase #4	$151.90	4.372%	$158.5411	$158.54	$158.55	$158.50
Purchase #5	$126.44	13.337%	$143.3033	$143.30	$143.30	$143.30
Purchase #6	$31.38	13.291%	$35.5507	$35.55	$35.55	$35.60
Purchase #7	$82.38	4.209%	$85.8474	$85.85	$85.85	$85.80
7 purchase totals =	$607.04		$661.7797	$661.78	$661.75	$661.80