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	$27.60	5.291%	$29.0603	$29.06	$29.05	$29.10
Purchase #2	$124.40	10.546%	$137.5192	$137.52	$137.50	$137.50
Purchase #3	$193.75	11.387%	$215.8123	$215.81	$215.80	$215.80
Purchase #4	$71.74	9.457%	$78.5245	$78.52	$78.50	$78.50
Purchase #5	$160.89	6.522%	$171.3832	$171.38	$171.40	$171.40
Purchase #6	$58.57	13.140%	$66.2661	$66.27	$66.25	$66.30
Purchase #7	$35.72	3.751%	$37.0599	$37.06	$37.05	$37.10
7 purchase totals =	$672.67		$735.6255	$735.62	$735.55	$735.70