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	$103.66	12.455%	$116.5709	$116.57	$116.55	$116.60
Purchase #2	$43.42	13.291%	$49.191	$49.19	$49.20	$49.20
Purchase #3	$87.38	3.114%	$90.101	$90.10	$90.10	$90.10
Purchase #4	$27.96	5.583%	$29.521	$29.52	$29.50	$29.50
Purchase #5	$126.72	12.388%	$142.4181	$142.42	$142.40	$142.40
Purchase #6	$195.67	13.868%	$222.8055	$222.81	$222.80	$222.80
Purchase #7	$231.68	7.802%	$249.7557	$249.76	$249.75	$249.80
7 purchase totals =	$816.49		$900.3632	$900.37	$900.30	$900.40