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	$8.41	12.619%	$9.4713	$9.47	$9.45	$9.50
Purchase #2	$115.85	6.515%	$123.3976	$123.40	$123.40	$123.40
Purchase #3	$229.52	5.278%	$241.6341	$241.63	$241.65	$241.60
Purchase #4	$115.59	13.773%	$131.5102	$131.51	$131.50	$131.50
Purchase #5	$39.96	11.714%	$44.6409	$44.64	$44.65	$44.60
Purchase #6	$105.79	10.435%	$116.8292	$116.83	$116.85	$116.80
Purchase #7	$198.33	13.623%	$225.3485	$225.35	$225.35	$225.30
7 purchase totals =	$813.45		$892.8318	$892.83	$892.85	$892.70