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	$8.62	13.870%	$9.8156	$9.82	$9.80	$9.80
Purchase #2	$54.86	12.726%	$61.8415	$61.84	$61.85	$61.80
Purchase #3	$45.94	12.819%	$51.829	$51.83	$51.85	$51.80
Purchase #4	$25.88	13.483%	$29.3694	$29.37	$29.35	$29.40
Purchase #5	$249.43	11.556%	$278.2541	$278.25	$278.25	$278.30
Purchase #6	$115.99	13.113%	$131.1998	$131.20	$131.20	$131.20
Purchase #7	$39.81	6.792%	$42.5139	$42.51	$42.50	$42.50
7 purchase totals =	$540.53		$604.8233	$604.82	$604.80	$604.80