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 $235.48   11.246%   $261.9621   $261.96   $261.95   $262.00  
  Purchase #2 $68.63   11.190%   $76.3097   $76.31   $76.30   $76.30  
  Purchase #3 $218.49   11.235%   $243.0374   $243.04   $243.05   $243.00  
  Purchase #4 $105.80   3.695%   $109.7093   $109.71   $109.70   $109.70  
  Purchase #5 $154.32   9.859%   $169.5344   $169.53   $169.55   $169.50  
  Purchase #6 $230.39   4.524%   $240.8128   $240.81   $240.80   $240.80  
  Purchase #7 $31.55   8.863%   $34.3463   $34.35   $34.35   $34.30  
  7 purchase totals = $1,044.66       $1,135.7120   $1,135.71   $1,135.70   $1,135.60