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 $84.96   10.188%   $93.6157   $93.62   $93.60   $93.60  
  Purchase #2 $246.83   6.110%   $261.9113   $261.91   $261.90   $261.90  
  Purchase #3 $86.60   3.559%   $89.6821   $89.68   $89.70   $89.70  
  Purchase #4 $88.87   5.274%   $93.557   $93.56   $93.55   $93.60  
  Purchase #5 $208.69   12.542%   $234.8639   $234.86   $234.85   $234.90  
  Purchase #6 $66.96   11.492%   $74.655   $74.66   $74.65   $74.70  
  Purchase #7 $247.84   3.177%   $255.7139   $255.71   $255.70   $255.70  
  7 purchase totals = $1,030.75       $1,103.9989   $1,104.00   $1,103.95   $1,104.10