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	$249.35	11.672%	$278.4541	$278.45	$278.45	$278.50
Purchase #2	$130.43	9.181%	$142.4048	$142.40	$142.40	$142.40
Purchase #3	$236.60	8.660%	$257.0896	$257.09	$257.10	$257.10
Purchase #4	$121.48	8.265%	$131.5203	$131.52	$131.50	$131.50
Purchase #5	$151.77	13.631%	$172.4578	$172.46	$172.45	$172.50
Purchase #6	$239.77	5.813%	$253.7078	$253.71	$253.70	$253.70
Purchase #7	$90.85	8.488%	$98.5613	$98.56	$98.55	$98.60
7 purchase totals =	$1,220.25		$1,334.1957	$1,334.19	$1,334.15	$1,334.30