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	$69.82	12.340%	$78.4358	$78.44	$78.45	$78.40
Purchase #2	$105.74	6.436%	$112.5454	$112.55	$112.55	$112.50
Purchase #3	$171.68	8.495%	$186.2642	$186.26	$186.25	$186.30
Purchase #4	$75.75	10.369%	$83.6045	$83.60	$83.60	$83.60
Purchase #5	$99.42	3.354%	$102.7545	$102.75	$102.75	$102.80
Purchase #6	$75.56	4.486%	$78.9496	$78.95	$78.95	$78.90
Purchase #7	$60.71	9.535%	$66.4987	$66.50	$66.50	$66.50
7 purchase totals =	$658.68		$709.0527	$709.05	$709.05	$709.00