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 $31.53   6.682%   $33.6368   $33.64   $33.65   $33.60  
  Purchase #2 $241.42   8.146%   $261.0861   $261.09   $261.10   $261.10  
  Purchase #3 $94.34   13.611%   $107.1806   $107.18   $107.20   $107.20  
  Purchase #4 $127.36   11.386%   $141.8612   $141.86   $141.85   $141.90  
  Purchase #5 $58.88   6.281%   $62.5783   $62.58   $62.60   $62.60  
  Purchase #6 $250.71   9.677%   $274.9712   $274.97   $274.95   $275.00  
  Purchase #7 $99.79   5.850%   $105.6277   $105.63   $105.65   $105.60  
  7 purchase totals = $904.03       $986.9419   $986.95   $987.00   $987.00