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 $179.84   12.850%   $202.9494   $202.95   $202.95   $202.90  
  Purchase #2 $240.99   10.451%   $266.1759   $266.18   $266.20   $266.20  
  Purchase #3 $114.39   9.504%   $125.2616   $125.26   $125.25   $125.30  
  Purchase #4 $33.28   13.359%   $37.7259   $37.73   $37.75   $37.70  
  Purchase #5 $125.77   8.175%   $136.0517   $136.05   $136.05   $136.10  
  Purchase #6 $161.81   10.874%   $179.4052   $179.41   $179.40   $179.40  
  Purchase #7 $246.64   3.854%   $256.1455   $256.15   $256.15   $256.10  
  7 purchase totals = $1,102.72       $1,203.7152   $1,203.73   $1,203.75   $1,203.70