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	$21.67	13.177%	$24.5255	$24.53	$24.55	$24.50
Purchase #2	$76.47	7.699%	$82.3574	$82.36	$82.35	$82.40
Purchase #3	$178.48	13.479%	$202.5373	$202.54	$202.55	$202.50
Purchase #4	$109.40	13.605%	$124.2839	$124.28	$124.30	$124.30
Purchase #5	$76.54	7.677%	$82.416	$82.42	$82.40	$82.40
Purchase #6	$215.37	10.823%	$238.6795	$238.68	$238.70	$238.70
Purchase #7	$206.27	8.509%	$223.8215	$223.82	$223.80	$223.80
7 purchase totals =	$884.20		$978.6211	$978.63	$978.65	$978.60