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	$29.48	13.462%	$33.4486	$33.45	$33.45	$33.40
Purchase #2	$133.59	3.162%	$137.8141	$137.81	$137.80	$137.80
Purchase #3	$82.56	8.842%	$89.86	$89.86	$89.85	$89.90
Purchase #4	$46.56	8.651%	$50.5879	$50.59	$50.60	$50.60
Purchase #5	$121.49	8.187%	$131.4364	$131.44	$131.45	$131.40
Purchase #6	$245.64	4.245%	$256.0674	$256.07	$256.05	$256.10
Purchase #7	$9.68	10.605%	$10.7066	$10.71	$10.70	$10.70
7 purchase totals =	$669.00		$709.9210	$709.93	$709.90	$709.90