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	$40.87	4.836%	$42.8465	$42.85	$42.85	$42.80
Purchase #2	$220.87	9.226%	$241.2475	$241.25	$241.25	$241.20
Purchase #3	$163.76	6.557%	$174.4977	$174.50	$174.50	$174.50
Purchase #4	$179.83	11.286%	$200.1256	$200.13	$200.15	$200.10
Purchase #5	$11.98	11.329%	$13.3372	$13.34	$13.35	$13.30
Purchase #6	$139.87	7.545%	$150.4232	$150.42	$150.40	$150.40
Purchase #7	$95.62	9.625%	$104.8234	$104.82	$104.80	$104.80
7 purchase totals =	$852.80		$927.3011	$927.31	$927.30	$927.10