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	$231.75	6.774%	$247.4487	$247.45	$247.45	$247.40
Purchase #2	$114.95	7.330%	$123.3758	$123.38	$123.40	$123.40
Purchase #3	$176.72	11.156%	$196.4349	$196.43	$196.45	$196.40
Purchase #4	$146.34	5.720%	$154.7106	$154.71	$154.70	$154.70
Purchase #5	$135.90	3.368%	$140.4771	$140.48	$140.50	$140.50
Purchase #6	$175.73	6.359%	$186.9047	$186.90	$186.90	$186.90
Purchase #7	$211.32	11.452%	$235.5204	$235.52	$235.50	$235.50
7 purchase totals =	$1,192.71		$1,284.8722	$1,284.87	$1,284.90	$1,284.80