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 $245.36   6.584%   $261.5145   $261.51   $261.50   $261.50  
  Purchase #2 $156.72   5.135%   $164.7676   $164.77   $164.75   $164.80  
  Purchase #3 $43.99   11.762%   $49.1641   $49.16   $49.15   $49.20  
  Purchase #4 $110.81   10.307%   $122.2312   $122.23   $122.25   $122.20  
  Purchase #5 $99.90   8.710%   $108.6013   $108.60   $108.60   $108.60  
  Purchase #6 $200.70   6.192%   $213.1273   $213.13   $213.15   $213.10  
  Purchase #7 $86.66   7.255%   $92.9472   $92.95   $92.95   $92.90  
  7 purchase totals = $944.14       $1,012.3532   $1,012.35   $1,012.35   $1,012.30