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	$39.27	6.602%	$41.8626	$41.86	$41.85	$41.90
Purchase #2	$64.81	12.565%	$72.9534	$72.95	$72.95	$73.00
Purchase #3	$20.37	13.729%	$23.1666	$23.17	$23.15	$23.20
Purchase #4	$116.80	12.685%	$131.6161	$131.62	$131.60	$131.60
Purchase #5	$44.53	13.577%	$50.5758	$50.58	$50.60	$50.60
Purchase #6	$47.89	4.257%	$49.9287	$49.93	$49.95	$49.90
Purchase #7	$83.86	3.387%	$86.7003	$86.70	$86.70	$86.70
7 purchase totals =	$417.53		$456.8035	$456.81	$456.80	$456.90