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	$13.96	10.367%	$15.4072	$15.41	$15.40	$15.40
Purchase #2	$225.29	13.532%	$255.7762	$255.78	$255.80	$255.80
Purchase #3	$39.29	3.782%	$40.7759	$40.78	$40.80	$40.80
Purchase #4	$74.75	3.466%	$77.3408	$77.34	$77.35	$77.30
Purchase #5	$203.87	5.785%	$215.6639	$215.66	$215.65	$215.70
Purchase #6	$237.26	10.432%	$262.011	$262.01	$262.00	$262.00
Purchase #7	$163.65	5.396%	$172.4806	$172.48	$172.50	$172.50
7 purchase totals =	$958.07		$1,039.4556	$1,039.46	$1,039.50	$1,039.50