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	$150.64	11.823%	$168.4502	$168.45	$168.45	$168.50
Purchase #2	$241.64	10.550%	$267.133	$267.13	$267.15	$267.10
Purchase #3	$136.64	6.430%	$145.426	$145.43	$145.45	$145.40
Purchase #4	$176.59	7.806%	$190.3746	$190.37	$190.35	$190.40
Purchase #5	$158.51	10.206%	$174.6875	$174.69	$174.70	$174.70
Purchase #6	$138.51	11.762%	$154.8015	$154.80	$154.80	$154.80
Purchase #7	$82.79	9.716%	$90.8339	$90.83	$90.85	$90.80
7 purchase totals =	$1,085.32		$1,191.7067	$1,191.70	$1,191.75	$1,191.70