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	$109.45	7.141%	$117.2658	$117.27	$117.25	$117.30
Purchase #2	$109.54	12.482%	$123.2128	$123.21	$123.20	$123.20
Purchase #3	$111.78	4.187%	$116.4602	$116.46	$116.45	$116.50
Purchase #4	$222.63	3.546%	$230.5245	$230.52	$230.50	$230.50
Purchase #5	$57.64	5.440%	$60.7756	$60.78	$60.80	$60.80
Purchase #6	$224.39	9.277%	$245.2067	$245.21	$245.20	$245.20
Purchase #7	$55.42	11.520%	$61.8044	$61.80	$61.80	$61.80
7 purchase totals =	$890.85		$955.2500	$955.25	$955.20	$955.30