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	$15.91	11.354%	$17.7164	$17.72	$17.70	$17.70
Purchase #2	$217.90	10.728%	$241.2763	$241.28	$241.30	$241.30
Purchase #3	$145.85	6.197%	$154.8883	$154.89	$154.90	$154.90
Purchase #4	$89.59	11.649%	$100.0263	$100.03	$100.05	$100.00
Purchase #5	$175.40	3.528%	$181.5881	$181.59	$181.60	$181.60
Purchase #6	$174.89	12.326%	$196.4469	$196.45	$196.45	$196.40
Purchase #7	$100.59	12.116%	$112.7775	$112.78	$112.80	$112.80
7 purchase totals =	$920.13		$1,004.7198	$1,004.74	$1,004.80	$1,004.70