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	$39.66	3.137%	$40.9041	$40.90	$40.90	$40.90
Purchase #2	$25.91	10.642%	$28.6673	$28.67	$28.65	$28.70
Purchase #3	$222.89	11.748%	$249.0751	$249.08	$249.10	$249.10
Purchase #4	$175.75	3.816%	$182.4566	$182.46	$182.45	$182.50
Purchase #5	$219.59	9.134%	$239.6474	$239.65	$239.65	$239.60
Purchase #6	$229.33	12.720%	$258.5008	$258.50	$258.50	$258.50
Purchase #7	$88.72	6.643%	$94.6137	$94.61	$94.60	$94.60
7 purchase totals =	$1,001.85		$1,093.8650	$1,093.87	$1,093.85	$1,093.90