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 $219.53   6.699%   $234.2363   $234.24   $234.25   $234.20  
  Purchase #2 $83.71   12.558%   $94.2223   $94.22   $94.20   $94.20  
  Purchase #3 $55.67   13.786%   $63.3447   $63.34   $63.35   $63.30  
  Purchase #4 $236.95   8.870%   $257.9675   $257.97   $257.95   $258.00  
  Purchase #5 $43.95   10.686%   $48.6465   $48.65   $48.65   $48.60  
  Purchase #6 $250.44   9.758%   $274.8779   $274.88   $274.90   $274.90  
  Purchase #7 $81.91   11.484%   $91.3165   $91.32   $91.30   $91.30  
  7 purchase totals = $972.16       $1,064.6117   $1,064.62   $1,064.60   $1,064.50