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	$77.72	11.409%	$86.5871	$86.59	$86.60	$86.60
Purchase #2	$63.81	8.874%	$69.4725	$69.47	$69.45	$69.50
Purchase #3	$140.25	13.277%	$158.871	$158.87	$158.85	$158.90
Purchase #4	$92.97	12.110%	$104.2287	$104.23	$104.25	$104.20
Purchase #5	$80.47	13.165%	$91.0639	$91.06	$91.05	$91.10
Purchase #6	$42.94	11.242%	$47.7673	$47.77	$47.75	$47.80
Purchase #7	$90.99	6.368%	$96.7842	$96.78	$96.80	$96.80
7 purchase totals =	$589.15		$654.7747	$654.77	$654.75	$654.90