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	$34.47	11.408%	$38.4023	$38.40	$38.40	$38.40
Purchase #2	$146.41	7.142%	$156.8666	$156.87	$156.85	$156.90
Purchase #3	$142.34	9.546%	$155.9278	$155.93	$155.95	$155.90
Purchase #4	$179.40	4.284%	$187.0855	$187.09	$187.10	$187.10
Purchase #5	$43.75	7.588%	$47.0698	$47.07	$47.05	$47.10
Purchase #6	$239.73	6.662%	$255.7008	$255.70	$255.70	$255.70
Purchase #7	$79.27	13.403%	$89.8946	$89.89	$89.90	$89.90
7 purchase totals =	$865.37		$930.9474	$930.95	$930.95	$931.00