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	$102.80	13.305%	$116.4775	$116.48	$116.50	$116.50
Purchase #2	$175.90	7.126%	$188.4346	$188.43	$188.45	$188.40
Purchase #3	$128.44	7.792%	$138.448	$138.45	$138.45	$138.40
Purchase #4	$37.84	5.233%	$39.8202	$39.82	$39.80	$39.80
Purchase #5	$65.90	12.156%	$73.9108	$73.91	$73.90	$73.90
Purchase #6	$51.52	11.464%	$57.4263	$57.43	$57.45	$57.40
Purchase #7	$192.95	3.858%	$200.394	$200.39	$200.40	$200.40
7 purchase totals =	$755.35		$814.9114	$814.91	$814.95	$814.80