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 $55.92   3.601%   $57.9337   $57.93   $57.95   $57.90  
  Purchase #2 $225.89   10.667%   $249.9857   $249.99   $250.00   $250.00  
  Purchase #3 $46.55   12.843%   $52.5284   $52.53   $52.55   $52.50  
  Purchase #4 $245.75   5.786%   $259.9691   $259.97   $259.95   $260.00  
  Purchase #5 $13.48   3.394%   $13.9375   $13.94   $13.95   $13.90  
  Purchase #6 $248.51   10.338%   $274.201   $274.20   $274.20   $274.20  
  Purchase #7 $110.95   7.395%   $119.1548   $119.15   $119.15   $119.20  
  7 purchase totals = $947.05       $1,027.7102   $1,027.71   $1,027.75   $1,027.70