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 $173.80   13.238%   $196.8076   $196.81   $196.80   $196.80  
  Purchase #2 $83.28   12.580%   $93.7566   $93.76   $93.75   $93.80  
  Purchase #3 $200.97   8.458%   $217.968   $217.97   $217.95   $218.00  
  Purchase #4 $60.86   6.312%   $64.7015   $64.70   $64.70   $64.70  
  Purchase #5 $94.60   10.847%   $104.8613   $104.86   $104.85   $104.90  
  Purchase #6 $105.75   8.695%   $114.945   $114.95   $114.95   $114.90  
  Purchase #7 $187.51   3.418%   $193.9191   $193.92   $193.90   $193.90  
  7 purchase totals = $906.77       $986.9591   $986.97   $986.90   $987.00