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	$19.45	6.786%	$20.7699	$20.77	$20.75	$20.80
Purchase #2	$91.75	12.688%	$103.3912	$103.39	$103.40	$103.40
Purchase #3	$18.30	10.451%	$20.2125	$20.21	$20.20	$20.20
Purchase #4	$140.48	9.743%	$154.167	$154.17	$154.15	$154.20
Purchase #5	$178.86	5.381%	$188.4845	$188.48	$188.50	$188.50
Purchase #6	$140.82	9.766%	$154.5725	$154.57	$154.55	$154.60
Purchase #7	$159.38	5.441%	$168.0519	$168.05	$168.05	$168.10
7 purchase totals =	$749.04		$809.6495	$809.64	$809.60	$809.80