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 $229.87   13.655%   $261.2587   $261.26   $261.25   $261.30  
  Purchase #2 $146.69   7.343%   $157.4614   $157.46   $157.45   $157.50  
  Purchase #3 $14.33   3.620%   $14.8487   $14.85   $14.85   $14.80  
  Purchase #4 $67.93   5.730%   $71.8224   $71.82   $71.80   $71.80  
  Purchase #5 $214.25   5.775%   $226.6229   $226.62   $226.60   $226.60  
  Purchase #6 $133.46   5.793%   $141.1913   $141.19   $141.20   $141.20  
  Purchase #7 $84.94   6.304%   $90.2946   $90.29   $90.30   $90.30  
  7 purchase totals = $891.47       $963.5000   $963.49   $963.45   $963.50