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 $245.46   6.606%   $261.6751   $261.68   $261.70   $261.70  
  Purchase #2 $118.72   6.361%   $126.2718   $126.27   $126.25   $126.30  
  Purchase #3 $141.34   7.358%   $151.7398   $151.74   $151.75   $151.70  
  Purchase #4 $22.89   11.789%   $25.5885   $25.59   $25.60   $25.60  
  Purchase #5 $249.81   12.351%   $280.664   $280.66   $280.65   $280.70  
  Purchase #6 $198.94   4.737%   $208.3638   $208.36   $208.35   $208.40  
  Purchase #7 $246.68   10.527%   $272.648   $272.65   $272.65   $272.60  
  7 purchase totals = $1,223.84       $1,326.9510   $1,326.95   $1,326.95   $1,327.00