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 $248.59   6.171%   $263.9305   $263.93   $263.95   $263.90  
  Purchase #2 $139.28   8.316%   $150.8625   $150.86   $150.85   $150.90  
  Purchase #3 $73.34   10.393%   $80.9622   $80.96   $80.95   $81.00  
  Purchase #4 $32.55   3.516%   $33.6945   $33.69   $33.70   $33.70  
  Purchase #5 $183.40   10.169%   $202.0499   $202.05   $202.05   $202.00  
  Purchase #6 $158.64   9.387%   $173.5315   $173.53   $173.55   $173.50  
  Purchase #7 $130.63   4.629%   $136.6769   $136.68   $136.70   $136.70  
  7 purchase totals = $966.43       $1,041.7080   $1,041.70   $1,041.75   $1,041.70