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 $54.63   12.529%   $61.4746   $61.47   $61.45   $61.50  
  Purchase #2 $245.83   5.721%   $259.8939   $259.89   $259.90   $259.90  
  Purchase #3 $101.97   3.329%   $105.3646   $105.36   $105.35   $105.40  
  Purchase #4 $233.86   5.704%   $247.1994   $247.20   $247.20   $247.20  
  Purchase #5 $225.80   12.179%   $253.3002   $253.30   $253.30   $253.30  
  Purchase #6 $66.71   3.529%   $69.0642   $69.06   $69.05   $69.10  
  Purchase #7 $15.77   10.757%   $17.4664   $17.47   $17.45   $17.50  
  7 purchase totals = $944.57       $1,013.7633   $1,013.75   $1,013.70   $1,013.90