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 $230.29   11.696%   $257.2247   $257.22   $257.20   $257.20  
  Purchase #2 $154.31   9.234%   $168.559   $168.56   $168.55   $168.60  
  Purchase #3 $185.65   8.579%   $201.5769   $201.58   $201.60   $201.60  
  Purchase #4 $216.26   9.468%   $236.7355   $236.74   $236.75   $236.70  
  Purchase #5 $105.58   8.226%   $114.265   $114.27   $114.25   $114.30  
  Purchase #6 $43.93   9.873%   $48.2672   $48.27   $48.25   $48.30  
  Purchase #7 $68.70   11.703%   $76.74   $76.74   $76.75   $76.70  
  7 purchase totals = $1,004.72       $1,103.3683   $1,103.38   $1,103.35   $1,103.40