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 $86.49   8.583%   $93.9134   $93.91   $93.90   $93.90  
  Purchase #2 $112.63   6.296%   $119.7212   $119.72   $119.70   $119.70  
  Purchase #3 $250.81   4.300%   $261.5948   $261.59   $261.60   $261.60  
  Purchase #4 $138.88   5.801%   $146.9364   $146.94   $146.95   $146.90  
  Purchase #5 $214.82   9.136%   $234.446   $234.45   $234.45   $234.40  
  Purchase #6 $202.90   3.108%   $209.2061   $209.21   $209.20   $209.20  
  Purchase #7 $60.46   9.402%   $66.1444   $66.14   $66.15   $66.10  
  7 purchase totals = $1,066.99       $1,131.9623   $1,131.96   $1,131.95   $1,131.80