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	$249.34	12.604%	$280.7668	$280.77	$280.75	$280.80
Purchase #2	$101.53	10.384%	$112.0729	$112.07	$112.05	$112.10
Purchase #3	$196.30	6.747%	$209.5444	$209.54	$209.55	$209.50
Purchase #4	$6.52	3.802%	$6.7679	$6.77	$6.75	$6.80
Purchase #5	$206.75	5.770%	$218.6795	$218.68	$218.70	$218.70
Purchase #6	$58.60	7.284%	$62.8684	$62.87	$62.85	$62.90
Purchase #7	$196.42	13.210%	$222.3671	$222.37	$222.35	$222.40
7 purchase totals =	$1,015.46		$1,113.0670	$1,113.07	$1,113.00	$1,113.20