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	$37.29	6.821%	$39.8336	$39.83	$39.85	$39.80
Purchase #2	$128.66	13.526%	$146.0626	$146.06	$146.05	$146.10
Purchase #3	$178.84	7.225%	$191.7612	$191.76	$191.75	$191.80
Purchase #4	$72.38	8.391%	$78.4534	$78.45	$78.45	$78.50
Purchase #5	$64.54	7.849%	$69.6057	$69.61	$69.60	$69.60
Purchase #6	$133.55	7.556%	$143.641	$143.64	$143.65	$143.60
Purchase #7	$13.55	13.349%	$15.3588	$15.36	$15.35	$15.40
7 purchase totals =	$628.81		$684.7163	$684.71	$684.70	$684.80