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 $60.93   12.327%   $68.4408   $68.44   $68.45   $68.40  
  Purchase #2 $249.42   3.305%   $257.6633   $257.66   $257.65   $257.70  
  Purchase #3 $8.29   5.208%   $8.7217   $8.72   $8.70   $8.70  
  Purchase #4 $15.60   11.757%   $17.4341   $17.43   $17.45   $17.40  
  Purchase #5 $250.94   3.565%   $259.886   $259.89   $259.90   $259.90  
  Purchase #6 $159.43   3.343%   $164.7597   $164.76   $164.75   $164.80  
  Purchase #7 $126.99   11.705%   $141.8542   $141.85   $141.85   $141.90  
  7 purchase totals = $871.60       $918.7598   $918.75   $918.75   $918.80