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 $245.93   8.536%   $266.9226   $266.92   $266.90   $266.90  
  Purchase #2 $199.48   6.599%   $212.6437   $212.64   $212.65   $212.60  
  Purchase #3 $173.27   11.498%   $193.1926   $193.19   $193.20   $193.20  
  Purchase #4 $250.85   4.697%   $262.6324   $262.63   $262.65   $262.60  
  Purchase #5 $41.87   3.553%   $43.3576   $43.36   $43.35   $43.40  
  Purchase #6 $68.68   13.371%   $77.8632   $77.86   $77.85   $77.90  
  Purchase #7 $191.42   6.338%   $203.5522   $203.55   $203.55   $203.60  
  7 purchase totals = $1,171.50       $1,260.1643   $1,260.15   $1,260.15   $1,260.20