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 $70.44   4.462%   $73.583   $73.58   $73.60   $73.60  
  Purchase #2 $15.68   11.603%   $17.4994   $17.50   $17.50   $17.50  
  Purchase #3 $208.77   10.640%   $230.9831   $230.98   $231.00   $231.00  
  Purchase #4 $128.69   3.407%   $133.0745   $133.07   $133.05   $133.10  
  Purchase #5 $37.34   13.321%   $42.3141   $42.31   $42.30   $42.30  
  Purchase #6 $163.38   13.786%   $185.9036   $185.90   $185.90   $185.90  
  Purchase #7 $233.54   3.691%   $242.16   $242.16   $242.15   $242.20  
  7 purchase totals = $857.84       $925.5177   $925.50   $925.50   $925.60