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	$220.60	13.697%	$250.8156	$250.82	$250.80	$250.80
Purchase #2	$51.66	3.569%	$53.5037	$53.50	$53.50	$53.50
Purchase #3	$207.90	9.853%	$228.3844	$228.38	$228.40	$228.40
Purchase #4	$95.71	9.286%	$104.5976	$104.60	$104.60	$104.60
Purchase #5	$113.75	9.785%	$124.8804	$124.88	$124.90	$124.90
Purchase #6	$249.45	5.387%	$262.8879	$262.89	$262.90	$262.90
Purchase #7	$129.52	12.636%	$145.8861	$145.89	$145.90	$145.90
7 purchase totals =	$1,068.59		$1,170.9557	$1,170.96	$1,171.00	$1,171.00