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	$226.99	13.393%	$257.3908	$257.39	$257.40	$257.40
Purchase #2	$182.69	9.725%	$200.4566	$200.46	$200.45	$200.50
Purchase #3	$75.46	4.582%	$78.9176	$78.92	$78.90	$78.90
Purchase #4	$234.28	8.277%	$253.6714	$253.67	$253.65	$253.70
Purchase #5	$78.71	4.282%	$82.0804	$82.08	$82.10	$82.10
Purchase #6	$239.65	7.227%	$256.9695	$256.97	$256.95	$257.00
Purchase #7	$158.76	13.434%	$180.0878	$180.09	$180.10	$180.10
7 purchase totals =	$1,196.54		$1,309.5741	$1,309.58	$1,309.55	$1,309.70