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 $179.46   13.642%   $203.9419   $203.94   $203.95   $203.90  
  Purchase #2 $51.55   3.662%   $53.4378   $53.44   $53.45   $53.40  
  Purchase #3 $102.95   5.561%   $108.675   $108.68   $108.70   $108.70  
  Purchase #4 $114.48   10.704%   $126.7339   $126.73   $126.75   $126.70  
  Purchase #5 $215.94   3.193%   $222.835   $222.84   $222.85   $222.80  
  Purchase #6 $160.56   11.823%   $179.543   $179.54   $179.55   $179.50  
  Purchase #7 $85.26   7.257%   $91.4473   $91.45   $91.45   $91.40  
  7 purchase totals = $910.20       $986.6139   $986.62   $986.70   $986.40