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	$103.61	12.843%	$116.9166	$116.92	$116.90	$116.90
Purchase #2	$17.34	10.787%	$19.2105	$19.21	$19.20	$19.20
Purchase #3	$14.38	5.866%	$15.2235	$15.22	$15.20	$15.20
Purchase #4	$40.34	5.566%	$42.5853	$42.59	$42.60	$42.60
Purchase #5	$92.54	13.314%	$104.8608	$104.86	$104.85	$104.90
Purchase #6	$119.96	10.326%	$132.3471	$132.35	$132.35	$132.30
Purchase #7	$68.46	5.854%	$72.4676	$72.47	$72.45	$72.50
7 purchase totals =	$456.63		$503.6114	$503.62	$503.55	$503.60