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	$100.74	7.309%	$108.1031	$108.10	$108.10	$108.10
Purchase #2	$207.88	13.542%	$236.0311	$236.03	$236.05	$236.00
Purchase #3	$75.52	3.738%	$78.3429	$78.34	$78.35	$78.30
Purchase #4	$132.87	4.870%	$139.3408	$139.34	$139.35	$139.30
Purchase #5	$51.98	6.773%	$55.5006	$55.50	$55.50	$55.50
Purchase #6	$192.77	10.526%	$213.061	$213.06	$213.05	$213.10
Purchase #7	$134.51	13.445%	$152.5949	$152.59	$152.60	$152.60
7 purchase totals =	$896.27		$982.9744	$982.96	$983.00	$982.90