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	$233.30	10.273%	$257.2669	$257.27	$257.25	$257.30
Purchase #2	$79.97	12.619%	$90.0614	$90.06	$90.05	$90.10
Purchase #3	$48.80	4.209%	$50.854	$50.85	$50.85	$50.90
Purchase #4	$234.64	9.287%	$256.431	$256.43	$256.45	$256.40
Purchase #5	$135.27	11.864%	$151.3184	$151.32	$151.30	$151.30
Purchase #6	$44.74	13.870%	$50.9454	$50.95	$50.95	$50.90
Purchase #7	$90.71	7.474%	$97.4897	$97.49	$97.50	$97.50
7 purchase totals =	$867.43		$954.3668	$954.37	$954.35	$954.40