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 $87.27   12.865%   $98.4973   $98.50   $98.50   $98.50  
  Purchase #2 $131.82   3.477%   $136.4034   $136.40   $136.40   $136.40  
  Purchase #3 $17.90   4.339%   $18.6767   $18.68   $18.70   $18.70  
  Purchase #4 $239.29   6.116%   $253.925   $253.93   $253.95   $253.90  
  Purchase #5 $245.80   4.856%   $257.736   $257.74   $257.75   $257.70  
  Purchase #6 $114.63   12.621%   $129.0975   $129.10   $129.10   $129.10  
  Purchase #7 $206.70   8.393%   $224.0483   $224.05   $224.05   $224.00  
  7 purchase totals = $1,043.41       $1,118.3842   $1,118.40   $1,118.45   $1,118.30