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	$63.81	13.757%	$72.5883	$72.59	$72.60	$72.60
Purchase #2	$237.28	7.729%	$255.6194	$255.62	$255.60	$255.60
Purchase #3	$182.49	13.605%	$207.3178	$207.32	$207.30	$207.30
Purchase #4	$62.83	13.212%	$71.1311	$71.13	$71.15	$71.10
Purchase #5	$116.68	6.777%	$124.5874	$124.59	$124.60	$124.60
Purchase #6	$82.35	10.222%	$90.7678	$90.77	$90.75	$90.80
Purchase #7	$250.54	6.144%	$265.9332	$265.93	$265.95	$265.90
7 purchase totals =	$995.98		$1,087.9450	$1,087.95	$1,087.95	$1,087.90