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	$244.85	11.835%	$273.828	$273.83	$273.85	$273.80
Purchase #2	$139.65	13.443%	$158.4231	$158.42	$158.40	$158.40
Purchase #3	$59.94	7.455%	$64.4085	$64.41	$64.40	$64.40
Purchase #4	$41.86	7.807%	$45.128	$45.13	$45.15	$45.10
Purchase #5	$38.87	13.754%	$44.2162	$44.22	$44.20	$44.20
Purchase #6	$231.67	10.671%	$256.3915	$256.39	$256.40	$256.40
Purchase #7	$148.84	6.149%	$157.9922	$157.99	$158.00	$158.00
7 purchase totals =	$905.68		$1,000.3875	$1,000.39	$1,000.40	$1,000.30