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 $182.94   10.237%   $201.6676   $201.67   $201.65   $201.70  
  Purchase #2 $97.28   7.544%   $104.6188   $104.62   $104.60   $104.60  
  Purchase #3 $101.57   12.725%   $114.4948   $114.49   $114.50   $114.50  
  Purchase #4 $27.74   13.307%   $31.4314   $31.43   $31.45   $31.40  
  Purchase #5 $160.54   7.809%   $173.0766   $173.08   $173.10   $173.10  
  Purchase #6 $46.31   9.859%   $50.8757   $50.88   $50.90   $50.90  
  Purchase #7 $98.69   9.851%   $108.412   $108.41   $108.40   $108.40  
  7 purchase totals = $715.07       $784.5769   $784.58   $784.60   $784.60