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	$156.61	12.588%	$176.3241	$176.32	$176.30	$176.30
Purchase #2	$25.97	12.229%	$29.1459	$29.15	$29.15	$29.10
Purchase #3	$241.78	6.289%	$256.9855	$256.99	$257.00	$257.00
Purchase #4	$12.67	5.402%	$13.3544	$13.35	$13.35	$13.40
Purchase #5	$27.87	13.747%	$31.7013	$31.70	$31.70	$31.70
Purchase #6	$74.54	10.870%	$82.6425	$82.64	$82.65	$82.60
Purchase #7	$179.30	9.392%	$196.1399	$196.14	$196.15	$196.10
7 purchase totals =	$718.74		$786.2936	$786.29	$786.30	$786.20