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 $63.29   4.823%   $66.3425   $66.34   $66.35   $66.30  
  Purchase #2 $203.51   5.129%   $213.948   $213.95   $213.95   $213.90  
  Purchase #3 $203.93   4.636%   $213.3842   $213.38   $213.40   $213.40  
  Purchase #4 $186.72   9.390%   $204.253   $204.25   $204.25   $204.30  
  Purchase #5 $29.73   3.189%   $30.6781   $30.68   $30.70   $30.70  
  Purchase #6 $21.83   10.191%   $24.0547   $24.05   $24.05   $24.10  
  Purchase #7 $66.33   9.591%   $72.6917   $72.69   $72.70   $72.70  
  7 purchase totals = $775.34       $825.3522   $825.34   $825.40   $825.40