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	$231.89	10.533%	$256.315	$256.32	$256.30	$256.30
Purchase #2	$229.59	12.600%	$258.5183	$258.52	$258.50	$258.50
Purchase #3	$138.57	12.640%	$156.0852	$156.09	$156.10	$156.10
Purchase #4	$215.27	6.333%	$228.903	$228.90	$228.90	$228.90
Purchase #5	$49.57	8.283%	$53.6759	$53.68	$53.70	$53.70
Purchase #6	$83.39	8.674%	$90.6232	$90.62	$90.60	$90.60
Purchase #7	$162.81	4.426%	$170.016	$170.02	$170.00	$170.00
7 purchase totals =	$1,111.09		$1,214.1366	$1,214.15	$1,214.10	$1,214.10