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 $140.99   7.294%   $151.2738   $151.27   $151.25   $151.30  
  Purchase #2 $204.48   12.281%   $229.5922   $229.59   $229.60   $229.60  
  Purchase #3 $217.83   5.331%   $229.4425   $229.44   $229.45   $229.40  
  Purchase #4 $198.33   5.224%   $208.6908   $208.69   $208.70   $208.70  
  Purchase #5 $209.38   13.164%   $236.9428   $236.94   $236.95   $236.90  
  Purchase #6 $228.87   8.530%   $248.3926   $248.39   $248.40   $248.40  
  Purchase #7 $91.68   4.216%   $95.5452   $95.55   $95.55   $95.50  
  7 purchase totals = $1,291.56       $1,399.8799   $1,399.87   $1,399.90   $1,399.80