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 $245.44   6.686%   $261.8501   $261.85   $261.85   $261.90  
  Purchase #2 $185.74   13.649%   $211.0917   $211.09   $211.10   $211.10  
  Purchase #3 $232.42   5.165%   $244.4245   $244.42   $244.40   $244.40  
  Purchase #4 $66.26   11.668%   $73.9912   $73.99   $74.00   $74.00  
  Purchase #5 $84.47   12.772%   $95.2585   $95.26   $95.25   $95.30  
  Purchase #6 $24.51   12.344%   $27.5355   $27.54   $27.55   $27.50  
  Purchase #7 $37.98   9.836%   $41.7157   $41.72   $41.70   $41.70  
  7 purchase totals = $876.82       $955.8672   $955.87   $955.85   $955.90