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 $182.90   8.656%   $198.7318   $198.73   $198.75   $198.70  
  Purchase #2 $248.54   4.434%   $259.5603   $259.56   $259.55   $259.60  
  Purchase #3 $225.95   4.804%   $236.8046   $236.80   $236.80   $236.80  
  Purchase #4 $198.38   5.319%   $208.9318   $208.93   $208.95   $208.90  
  Purchase #5 $29.96   11.474%   $33.3976   $33.40   $33.40   $33.40  
  Purchase #6 $137.59   12.345%   $154.5755   $154.58   $154.60   $154.60  
  Purchase #7 $235.61   7.465%   $253.1983   $253.20   $253.20   $253.20  
  7 purchase totals = $1,258.93       $1,345.1999   $1,345.20   $1,345.25   $1,345.20