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	$166.34	3.176%	$171.623	$171.62	$171.60	$171.60
Purchase #2	$245.96	12.860%	$277.5905	$277.59	$277.60	$277.60
Purchase #3	$162.78	9.837%	$178.7927	$178.79	$178.80	$178.80
Purchase #4	$59.48	12.349%	$66.8252	$66.83	$66.85	$66.80
Purchase #5	$105.96	12.834%	$119.5589	$119.56	$119.55	$119.60
Purchase #6	$212.75	10.594%	$235.2887	$235.29	$235.30	$235.30
Purchase #7	$230.75	3.280%	$238.3186	$238.32	$238.30	$238.30
7 purchase totals =	$1,184.02		$1,287.9976	$1,288.00	$1,288.00	$1,288.00