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 $70.81   8.639%   $76.9273   $76.93   $76.95   $76.90  
  Purchase #2 $32.92   8.127%   $35.5954   $35.60   $35.60   $35.60  
  Purchase #3 $106.73   7.575%   $114.8148   $114.81   $114.80   $114.80  
  Purchase #4 $95.70   10.824%   $106.0586   $106.06   $106.05   $106.10  
  Purchase #5 $231.47   7.390%   $248.5756   $248.58   $248.60   $248.60  
  Purchase #6 $126.82   9.171%   $138.4507   $138.45   $138.45   $138.50  
  Purchase #7 $88.76   9.665%   $97.3387   $97.34   $97.35   $97.30  
  7 purchase totals = $753.21       $817.7611   $817.77   $817.80   $817.80