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 $147.80   10.704%   $163.6205   $163.62   $163.60   $163.60  
  Purchase #2 $176.43   5.540%   $186.2042   $186.20   $186.20   $186.20  
  Purchase #3 $225.44   11.303%   $250.9215   $250.92   $250.90   $250.90  
  Purchase #4 $16.36   5.546%   $17.2673   $17.27   $17.25   $17.30  
  Purchase #5 $140.80   5.805%   $148.9734   $148.97   $148.95   $149.00  
  Purchase #6 $67.38   9.611%   $73.8559   $73.86   $73.85   $73.90  
  Purchase #7 $51.48   8.676%   $55.9464   $55.95   $55.95   $55.90  
  7 purchase totals = $825.69       $896.7892   $896.79   $896.70   $896.80