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	$47.67	13.515%	$54.1126	$54.11	$54.10	$54.10
Purchase #2	$166.86	4.802%	$174.8726	$174.87	$174.85	$174.90
Purchase #3	$38.47	6.238%	$40.8698	$40.87	$40.85	$40.90
Purchase #4	$80.86	7.720%	$87.1024	$87.10	$87.10	$87.10
Purchase #5	$190.37	13.174%	$215.4493	$215.45	$215.45	$215.40
Purchase #6	$66.76	10.630%	$73.8566	$73.86	$73.85	$73.90
Purchase #7	$55.47	12.621%	$62.4709	$62.47	$62.45	$62.50
7 purchase totals =	$646.46		$708.7342	$708.73	$708.65	$708.80