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 $246.33   8.613%   $267.5464   $267.55   $267.55   $267.50  
  Purchase #2 $144.80   8.319%   $156.8459   $156.85   $156.85   $156.80  
  Purchase #3 $164.54   11.869%   $184.0693   $184.07   $184.05   $184.10  
  Purchase #4 $14.62   13.526%   $16.5975   $16.60   $16.60   $16.60  
  Purchase #5 $235.71   5.239%   $248.0588   $248.06   $248.05   $248.10  
  Purchase #6 $87.88   8.198%   $95.0844   $95.08   $95.10   $95.10  
  Purchase #7 $17.46   9.136%   $19.0551   $19.06   $19.05   $19.10  
  7 purchase totals = $911.34       $987.2574   $987.27   $987.25   $987.30