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 $201.46   7.157%   $215.8785   $215.88   $215.90   $215.90  
  Purchase #2 $187.30   3.194%   $193.2824   $193.28   $193.30   $193.30  
  Purchase #3 $70.93   7.323%   $76.1242   $76.12   $76.10   $76.10  
  Purchase #4 $55.52   12.142%   $62.2612   $62.26   $62.25   $62.30  
  Purchase #5 $131.35   11.270%   $146.1531   $146.15   $146.15   $146.20  
  Purchase #6 $171.27   7.189%   $183.5826   $183.58   $183.60   $183.60  
  Purchase #7 $63.76   3.743%   $66.1465   $66.15   $66.15   $66.10  
  7 purchase totals = $881.59       $943.4285   $943.42   $943.45   $943.50