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	$21.82	12.509%	$24.5495	$24.55	$24.55	$24.50
Purchase #2	$109.77	12.397%	$123.3782	$123.38	$123.40	$123.40
Purchase #3	$205.86	7.416%	$221.1266	$221.13	$221.15	$221.10
Purchase #4	$135.83	9.174%	$148.291	$148.29	$148.30	$148.30
Purchase #5	$109.90	4.266%	$114.5883	$114.59	$114.60	$114.60
Purchase #6	$80.30	12.837%	$90.6081	$90.61	$90.60	$90.60
Purchase #7	$191.46	12.490%	$215.3734	$215.37	$215.35	$215.40
7 purchase totals =	$854.94		$937.9151	$937.92	$937.95	$937.90