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 $66.76   4.104%   $69.4998   $69.50   $69.50   $69.50  
  Purchase #2 $218.77   12.773%   $246.7135   $246.71   $246.70   $246.70  
  Purchase #3 $226.57   9.195%   $247.4031   $247.40   $247.40   $247.40  
  Purchase #4 $21.45   6.780%   $22.9043   $22.90   $22.90   $22.90  
  Purchase #5 $250.73   10.457%   $276.9488   $276.95   $276.95   $276.90  
  Purchase #6 $6.26   8.687%   $6.8038   $6.80   $6.80   $6.80  
  Purchase #7 $79.95   3.169%   $82.4836   $82.48   $82.50   $82.50  
  7 purchase totals = $870.49       $952.7569   $952.74   $952.75   $952.70