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 $43.94   7.759%   $47.3493   $47.35   $47.35   $47.30  
  Purchase #2 $129.69   10.454%   $143.2478   $143.25   $143.25   $143.20  
  Purchase #3 $235.88   9.622%   $258.5764   $258.58   $258.60   $258.60  
  Purchase #4 $164.55   5.839%   $174.1581   $174.16   $174.15   $174.20  
  Purchase #5 $176.28   8.719%   $191.6499   $191.65   $191.65   $191.60  
  Purchase #6 $216.57   13.488%   $245.781   $245.78   $245.80   $245.80  
  Purchase #7 $209.66   3.455%   $216.9038   $216.90   $216.90   $216.90  
  7 purchase totals = $1,176.57       $1,277.6663   $1,277.67   $1,277.70   $1,277.60