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 $161.59   13.391%   $183.2285   $183.23   $183.25   $183.20  
  Purchase #2 $23.36   13.686%   $26.557   $26.56   $26.55   $26.60  
  Purchase #3 $174.79   13.832%   $198.967   $198.97   $198.95   $199.00  
  Purchase #4 $132.56   3.110%   $136.6826   $136.68   $136.70   $136.70  
  Purchase #5 $234.70   11.295%   $261.2094   $261.21   $261.20   $261.20  
  Purchase #6 $51.86   8.363%   $56.1971   $56.20   $56.20   $56.20  
  Purchase #7 $196.47   3.395%   $203.1402   $203.14   $203.15   $203.10  
  7 purchase totals = $975.33       $1,065.9818   $1,065.99   $1,066.00   $1,066.00