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 $139.98   6.631%   $149.2621   $149.26   $149.25   $149.30  
  Purchase #2 $250.42   5.483%   $264.1505   $264.15   $264.15   $264.20  
  Purchase #3 $231.89   12.633%   $261.1847   $261.18   $261.20   $261.20  
  Purchase #4 $235.33   9.587%   $257.8911   $257.89   $257.90   $257.90  
  Purchase #5 $176.26   5.493%   $185.942   $185.94   $185.95   $185.90  
  Purchase #6 $169.43   10.314%   $186.905   $186.91   $186.90   $186.90  
  Purchase #7 $50.75   3.658%   $52.6064   $52.61   $52.60   $52.60  
  7 purchase totals = $1,254.06       $1,357.9418   $1,357.94   $1,357.95   $1,358.00