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	$38.46	10.597%	$42.5356	$42.54	$42.55	$42.50
Purchase #2	$182.42	9.411%	$199.5875	$199.59	$199.60	$199.60
Purchase #3	$218.95	10.503%	$241.9463	$241.95	$241.95	$241.90
Purchase #4	$95.32	5.163%	$100.2414	$100.24	$100.25	$100.20
Purchase #5	$37.52	12.603%	$42.2486	$42.25	$42.25	$42.20
Purchase #6	$216.37	9.690%	$237.3363	$237.34	$237.35	$237.30
Purchase #7	$123.66	4.394%	$129.0936	$129.09	$129.10	$129.10
7 purchase totals =	$912.70		$992.9893	$993.00	$993.05	$992.80