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	$246.71	13.679%	$280.4575	$280.46	$280.45	$280.50
Purchase #2	$122.68	9.150%	$133.9052	$133.91	$133.90	$133.90
Purchase #3	$126.87	8.661%	$137.8582	$137.86	$137.85	$137.90
Purchase #4	$98.47	8.510%	$106.8498	$106.85	$106.85	$106.80
Purchase #5	$117.74	12.761%	$132.7648	$132.76	$132.75	$132.80
Purchase #6	$44.79	5.557%	$47.279	$47.28	$47.30	$47.30
Purchase #7	$124.67	11.618%	$139.1542	$139.15	$139.15	$139.20
7 purchase totals =	$881.93		$978.2687	$978.27	$978.25	$978.40