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 $29.83   10.149%   $32.8574   $32.86   $32.85   $32.90  
  Purchase #2 $227.33   13.798%   $258.697   $258.70   $258.70   $258.70  
  Purchase #3 $158.79   11.421%   $176.9254   $176.93   $176.95   $176.90  
  Purchase #4 $97.81   6.745%   $104.4073   $104.41   $104.40   $104.40  
  Purchase #5 $22.92   8.508%   $24.87   $24.87   $24.85   $24.90  
  Purchase #6 $176.39   12.185%   $197.8831   $197.88   $197.90   $197.90  
  Purchase #7 $97.37   5.342%   $102.5715   $102.57   $102.55   $102.60  
  7 purchase totals = $810.44       $898.2117   $898.22   $898.20   $898.30