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	$56.98	11.326%	$63.4336	$63.43	$63.45	$63.40
Purchase #2	$111.29	10.539%	$123.0189	$123.02	$123.00	$123.00
Purchase #3	$245.65	5.441%	$259.0158	$259.02	$259.00	$259.00
Purchase #4	$100.99	3.769%	$104.7963	$104.80	$104.80	$104.80
Purchase #5	$20.83	4.823%	$21.8346	$21.83	$21.85	$21.80
Purchase #6	$152.84	7.621%	$164.4879	$164.49	$164.50	$164.50
Purchase #7	$236.76	7.856%	$255.3599	$255.36	$255.35	$255.40
7 purchase totals =	$925.34		$991.9470	$991.95	$991.95	$991.90