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	$232.66	11.258%	$258.8529	$258.85	$258.85	$258.90
Purchase #2	$227.27	8.255%	$246.0311	$246.03	$246.05	$246.00
Purchase #3	$83.55	7.165%	$89.5364	$89.54	$89.55	$89.50
Purchase #4	$215.80	9.835%	$237.0239	$237.02	$237.00	$237.00
Purchase #5	$155.81	10.599%	$172.3243	$172.32	$172.30	$172.30
Purchase #6	$51.89	5.553%	$54.7715	$54.77	$54.75	$54.80
Purchase #7	$35.40	13.563%	$40.2013	$40.20	$40.20	$40.20
7 purchase totals =	$1,002.38		$1,098.7414	$1,098.73	$1,098.70	$1,098.70