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 $136.86   12.762%   $154.3261   $154.33   $154.35   $154.30  
  Purchase #2 $237.64   10.250%   $261.9981   $262.00   $262.00   $262.00  
  Purchase #3 $75.83   5.135%   $79.7239   $79.72   $79.70   $79.70  
  Purchase #4 $78.88   13.626%   $89.6282   $89.63   $89.65   $89.60  
  Purchase #5 $247.66   5.222%   $260.5928   $260.59   $260.60   $260.60  
  Purchase #6 $117.71   5.449%   $124.124   $124.12   $124.10   $124.10  
  Purchase #7 $14.80   6.471%   $15.7577   $15.76   $15.75   $15.80  
  7 purchase totals = $909.38       $986.1508   $986.15   $986.15   $986.10