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 $60.74   8.128%   $65.6769   $65.68   $65.70   $65.70  
  Purchase #2 $15.26   5.106%   $16.0392   $16.04   $16.05   $16.00  
  Purchase #3 $214.47   9.397%   $234.6237   $234.62   $234.60   $234.60  
  Purchase #4 $70.74   11.869%   $79.1361   $79.14   $79.15   $79.10  
  Purchase #5 $77.48   6.609%   $82.6007   $82.60   $82.60   $82.60  
  Purchase #6 $196.56   5.630%   $207.6263   $207.63   $207.65   $207.60  
  Purchase #7 $20.75   8.814%   $22.5789   $22.58   $22.60   $22.60  
  7 purchase totals = $656.00       $708.2818   $708.29   $708.35   $708.20