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 $232.62   12.475%   $261.6393   $261.64   $261.65   $261.60  
  Purchase #2 $140.69   8.477%   $152.6163   $152.62   $152.60   $152.60  
  Purchase #3 $79.62   9.153%   $86.9076   $86.91   $86.90   $86.90  
  Purchase #4 $223.63   9.664%   $245.2416   $245.24   $245.25   $245.20  
  Purchase #5 $19.53   12.451%   $21.9617   $21.96   $21.95   $22.00  
  Purchase #6 $144.25   4.409%   $150.61   $150.61   $150.60   $150.60  
  Purchase #7 $26.91   13.661%   $30.5862   $30.59   $30.60   $30.60  
  7 purchase totals = $867.25       $949.5627   $949.57   $949.55   $949.50