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	$239.68	7.646%	$258.0059	$258.01	$258.00	$258.00
Purchase #2	$203.69	10.390%	$224.8534	$224.85	$224.85	$224.90
Purchase #3	$137.47	11.696%	$153.5485	$153.55	$153.55	$153.50
Purchase #4	$183.95	6.866%	$196.58	$196.58	$196.60	$196.60
Purchase #5	$109.73	4.835%	$115.0354	$115.04	$115.05	$115.00
Purchase #6	$49.66	10.412%	$54.8306	$54.83	$54.85	$54.80
Purchase #7	$39.62	10.691%	$43.8558	$43.86	$43.85	$43.90
7 purchase totals =	$963.80		$1,046.7096	$1,046.72	$1,046.75	$1,046.70