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 $247.80   10.712%   $274.3443   $274.34   $274.35   $274.30  
  Purchase #2 $88.58   13.291%   $100.3532   $100.35   $100.35   $100.40  
  Purchase #3 $104.39   8.202%   $112.9521   $112.95   $112.95   $113.00  
  Purchase #4 $32.28   11.591%   $36.0216   $36.02   $36.00   $36.00  
  Purchase #5 $109.76   4.347%   $114.5313   $114.53   $114.55   $114.50  
  Purchase #6 $25.89   3.546%   $26.8081   $26.81   $26.80   $26.80  
  Purchase #7 $218.48   12.847%   $246.5481   $246.55   $246.55   $246.50  
  7 purchase totals = $827.18       $911.5587   $911.55   $911.55   $911.50