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 $49.27   13.553%   $55.9476   $55.95   $55.95   $55.90  
  Purchase #2 $126.81   4.536%   $132.5621   $132.56   $132.55   $132.60  
  Purchase #3 $100.59   8.649%   $109.29   $109.29   $109.30   $109.30  
  Purchase #4 $85.83   11.329%   $95.5537   $95.55   $95.55   $95.60  
  Purchase #5 $249.57   4.701%   $261.3023   $261.30   $261.30   $261.30  
  Purchase #6 $67.80   12.393%   $76.2025   $76.20   $76.20   $76.20  
  Purchase #7 $211.44   9.379%   $231.271   $231.27   $231.25   $231.30  
  7 purchase totals = $891.31       $962.1292   $962.12   $962.10   $962.20