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	$78.55	3.776%	$81.516	$81.52	$81.50	$81.50
Purchase #2	$20.97	4.557%	$21.9256	$21.93	$21.95	$21.90
Purchase #3	$250.43	11.846%	$280.0959	$280.10	$280.10	$280.10
Purchase #4	$233.62	9.522%	$255.8653	$255.87	$255.85	$255.90
Purchase #5	$89.42	4.430%	$93.3813	$93.38	$93.40	$93.40
Purchase #6	$127.35	9.453%	$139.3884	$139.39	$139.40	$139.40
Purchase #7	$139.40	11.133%	$154.9194	$154.92	$154.90	$154.90
7 purchase totals =	$939.74		$1,027.0919	$1,027.11	$1,027.10	$1,027.10