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	$137.65	3.529%	$142.5077	$142.51	$142.50	$142.50
Purchase #2	$215.40	4.646%	$225.4075	$225.41	$225.40	$225.40
Purchase #3	$124.52	9.808%	$136.7329	$136.73	$136.75	$136.70
Purchase #4	$109.42	6.431%	$116.4568	$116.46	$116.45	$116.50
Purchase #5	$123.94	12.661%	$139.632	$139.63	$139.65	$139.60
Purchase #6	$74.59	12.383%	$83.8265	$83.83	$83.85	$83.80
Purchase #7	$87.71	13.259%	$99.3395	$99.34	$99.35	$99.30
7 purchase totals =	$873.23		$943.9029	$943.91	$943.95	$943.80