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	$35.93	13.641%	$40.8312	$40.83	$40.85	$40.80
Purchase #2	$60.73	4.690%	$63.5782	$63.58	$63.60	$63.60
Purchase #3	$55.76	12.745%	$62.8666	$62.87	$62.85	$62.90
Purchase #4	$227.38	6.641%	$242.4803	$242.48	$242.50	$242.50
Purchase #5	$178.32	5.854%	$188.7589	$188.76	$188.75	$188.80
Purchase #6	$151.50	10.748%	$167.7832	$167.78	$167.80	$167.80
Purchase #7	$194.46	8.871%	$211.7105	$211.71	$211.70	$211.70
7 purchase totals =	$904.08		$978.0089	$978.01	$978.05	$978.10