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	$50.53	13.741%	$57.4733	$57.47	$57.45	$57.50
Purchase #2	$183.90	4.308%	$191.8224	$191.82	$191.80	$191.80
Purchase #3	$206.54	10.209%	$227.6257	$227.63	$227.65	$227.60
Purchase #4	$11.79	9.611%	$12.9231	$12.92	$12.90	$12.90
Purchase #5	$249.91	7.780%	$269.353	$269.35	$269.35	$269.40
Purchase #6	$146.32	3.143%	$150.9188	$150.92	$150.90	$150.90
Purchase #7	$156.75	3.120%	$161.6406	$161.64	$161.65	$161.60
7 purchase totals =	$1,005.74		$1,071.7569	$1,071.75	$1,071.70	$1,071.70