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	$240.82	6.579%	$256.6635	$256.66	$256.65	$256.70
Purchase #2	$49.95	7.193%	$53.5429	$53.54	$53.55	$53.50
Purchase #3	$210.35	8.126%	$227.443	$227.44	$227.45	$227.40
Purchase #4	$38.25	4.122%	$39.8267	$39.83	$39.85	$39.80
Purchase #5	$31.39	7.181%	$33.6441	$33.64	$33.65	$33.60
Purchase #6	$202.34	6.612%	$215.7187	$215.72	$215.70	$215.70
Purchase #7	$245.36	11.200%	$272.8403	$272.84	$272.85	$272.80
7 purchase totals =	$1,018.46		$1,099.6792	$1,099.67	$1,099.70	$1,099.50