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 $76.55   10.139%   $84.3114   $84.31   $84.30   $84.30  
  Purchase #2 $242.80   8.283%   $262.9111   $262.91   $262.90   $262.90  
  Purchase #3 $50.62   7.816%   $54.5765   $54.58   $54.60   $54.60  
  Purchase #4 $146.81   12.669%   $165.4094   $165.41   $165.40   $165.40  
  Purchase #5 $225.66   4.848%   $236.6   $236.60   $236.60   $236.60  
  Purchase #6 $158.48   9.815%   $174.0348   $174.03   $174.05   $174.00  
  Purchase #7 $84.79   5.431%   $89.3949   $89.39   $89.40   $89.40  
  7 purchase totals = $985.71       $1,067.2381   $1,067.23   $1,067.25   $1,067.20