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 $116.69   11.873%   $130.5446   $130.54   $130.55   $130.50  
  Purchase #2 $51.47   13.832%   $58.5893   $58.59   $58.60   $58.60  
  Purchase #3 $59.41   5.500%   $62.6776   $62.68   $62.70   $62.70  
  Purchase #4 $50.84   13.527%   $57.7171   $57.72   $57.70   $57.70  
  Purchase #5 $205.77   6.241%   $218.6121   $218.61   $218.60   $218.60  
  Purchase #6 $117.67   4.524%   $122.9934   $122.99   $123.00   $123.00  
  Purchase #7 $198.32   6.189%   $210.594   $210.59   $210.60   $210.60  
  7 purchase totals = $800.17       $861.7281   $861.72   $861.75   $861.70