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	$47.35	12.720%	$53.3729	$53.37	$53.35	$53.40
Purchase #2	$148.52	10.822%	$164.5928	$164.59	$164.60	$164.60
Purchase #3	$149.92	9.737%	$164.5177	$164.52	$164.50	$164.50
Purchase #4	$128.70	4.630%	$134.6588	$134.66	$134.65	$134.70
Purchase #5	$88.93	4.509%	$92.9399	$92.94	$92.95	$92.90
Purchase #6	$174.98	8.165%	$189.2671	$189.27	$189.25	$189.30
Purchase #7	$21.93	13.649%	$24.9232	$24.92	$24.90	$24.90
7 purchase totals =	$760.33		$824.2724	$824.27	$824.20	$824.30