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 $207.68   13.420%   $235.5507   $235.55   $235.55   $235.60  
  Purchase #2 $38.56   7.356%   $41.3965   $41.40   $41.40   $41.40  
  Purchase #3 $146.42   7.427%   $157.2946   $157.29   $157.30   $157.30  
  Purchase #4 $24.48   12.263%   $27.482   $27.48   $27.50   $27.50  
  Purchase #5 $104.76   9.630%   $114.8484   $114.85   $114.85   $114.80  
  Purchase #6 $171.36   3.698%   $177.6969   $177.70   $177.70   $177.70  
  Purchase #7 $13.35   8.454%   $14.4786   $14.48   $14.50   $14.50  
  7 purchase totals = $706.61       $768.7477   $768.75   $768.80   $768.80