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 $124.97   13.539%   $141.8897   $141.89   $141.90   $141.90  
  Purchase #2 $201.44   6.172%   $213.8729   $213.87   $213.85   $213.90  
  Purchase #3 $167.93   4.627%   $175.7001   $175.70   $175.70   $175.70  
  Purchase #4 $127.97   3.563%   $132.5296   $132.53   $132.55   $132.50  
  Purchase #5 $220.68   6.465%   $234.947   $234.95   $234.95   $234.90  
  Purchase #6 $28.57   5.492%   $30.1391   $30.14   $30.15   $30.10  
  Purchase #7 $52.89   6.319%   $56.2321   $56.23   $56.25   $56.20  
  7 purchase totals = $924.45       $985.3105   $985.31   $985.35   $985.20