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 $48.81   13.785%   $55.5385   $55.54   $55.55   $55.50  
  Purchase #2 $118.85   3.515%   $123.0276   $123.03   $123.05   $123.00  
  Purchase #3 $247.62   12.328%   $278.1466   $278.15   $278.15   $278.10  
  Purchase #4 $206.62   12.786%   $233.0384   $233.04   $233.05   $233.00  
  Purchase #5 $114.26   4.666%   $119.5914   $119.59   $119.60   $119.60  
  Purchase #6 $126.33   3.483%   $130.7301   $130.73   $130.75   $130.70  
  Purchase #7 $22.78   7.871%   $24.573   $24.57   $24.55   $24.60  
  7 purchase totals = $885.27       $964.6456   $964.65   $964.70   $964.50