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	$26.47	3.800%	$27.4759	$27.48	$27.50	$27.50
Purchase #2	$249.62	12.473%	$280.7551	$280.76	$280.75	$280.80
Purchase #3	$141.89	12.466%	$159.578	$159.58	$159.60	$159.60
Purchase #4	$221.93	6.472%	$236.2933	$236.29	$236.30	$236.30
Purchase #5	$150.40	7.486%	$161.6589	$161.66	$161.65	$161.70
Purchase #6	$17.64	9.542%	$19.3232	$19.32	$19.30	$19.30
Purchase #7	$111.59	10.389%	$123.1831	$123.18	$123.20	$123.20
7 purchase totals =	$919.54		$1,008.2675	$1,008.27	$1,008.30	$1,008.40