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	$129.59	10.334%	$142.9818	$142.98	$143.00	$143.00
Purchase #2	$103.45	13.458%	$117.3723	$117.37	$117.35	$117.40
Purchase #3	$72.83	9.846%	$80.0008	$80.00	$80.00	$80.00
Purchase #4	$84.27	8.671%	$91.5771	$91.58	$91.60	$91.60
Purchase #5	$55.78	12.738%	$62.8853	$62.89	$62.90	$62.90
Purchase #6	$143.32	11.839%	$160.2877	$160.29	$160.30	$160.30
Purchase #7	$17.34	9.133%	$18.9237	$18.92	$18.90	$18.90
7 purchase totals =	$606.58		$674.0287	$674.03	$674.05	$674.10