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	$36.34	9.707%	$39.8675	$39.87	$39.85	$39.90
Purchase #2	$179.70	7.288%	$192.7965	$192.80	$192.80	$192.80
Purchase #3	$115.42	6.420%	$122.83	$122.83	$122.85	$122.80
Purchase #4	$42.32	7.421%	$45.4606	$45.46	$45.45	$45.50
Purchase #5	$242.53	12.667%	$273.2513	$273.25	$273.25	$273.30
Purchase #6	$97.75	6.858%	$104.4537	$104.45	$104.45	$104.50
Purchase #7	$240.46	6.516%	$256.1284	$256.13	$256.15	$256.10
7 purchase totals =	$954.52		$1,034.7880	$1,034.79	$1,034.80	$1,034.90