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 $62.28   13.357%   $70.5987   $70.60   $70.60   $70.60  
  Purchase #2 $51.93   8.636%   $56.4147   $56.41   $56.40   $56.40  
  Purchase #3 $139.32   3.525%   $144.231   $144.23   $144.25   $144.20  
  Purchase #4 $179.93   7.187%   $192.8616   $192.86   $192.85   $192.90  
  Purchase #5 $234.26   4.431%   $244.6401   $244.64   $244.65   $244.60  
  Purchase #6 $138.83   9.757%   $152.3756   $152.38   $152.40   $152.40  
  Purchase #7 $126.60   9.408%   $138.5105   $138.51   $138.50   $138.50  
  7 purchase totals = $933.15       $999.6322   $999.63   $999.65   $999.60