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 $201.92   13.716%   $229.6153   $229.62   $229.60   $229.60  
  Purchase #2 $49.93   11.433%   $55.6385   $55.64   $55.65   $55.60  
  Purchase #3 $197.56   8.198%   $213.756   $213.76   $213.75   $213.80  
  Purchase #4 $248.25   5.278%   $261.3526   $261.35   $261.35   $261.40  
  Purchase #5 $71.26   7.484%   $76.5931   $76.59   $76.60   $76.60  
  Purchase #6 $199.87   3.600%   $207.0653   $207.07   $207.05   $207.10  
  Purchase #7 $182.79   9.752%   $200.6157   $200.62   $200.60   $200.60  
  7 purchase totals = $1,151.58       $1,244.6365   $1,244.65   $1,244.60   $1,244.70