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	$102.87	10.421%	$113.5901	$113.59	$113.60	$113.60
Purchase #2	$15.83	10.376%	$17.4725	$17.47	$17.45	$17.50
Purchase #3	$177.86	7.792%	$191.7189	$191.72	$191.70	$191.70
Purchase #4	$83.48	4.105%	$86.9069	$86.91	$86.90	$86.90
Purchase #5	$23.59	5.269%	$24.833	$24.83	$24.85	$24.80
Purchase #6	$160.37	13.779%	$182.4674	$182.47	$182.45	$182.50
Purchase #7	$21.51	12.638%	$24.2284	$24.23	$24.25	$24.20
7 purchase totals =	$585.51		$641.2172	$641.22	$641.20	$641.20