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 $124.60   4.859%   $130.6543   $130.65   $130.65   $130.70  
  Purchase #2 $47.64   6.827%   $50.8924   $50.89   $50.90   $50.90  
  Purchase #3 $104.76   3.870%   $108.8142   $108.81   $108.80   $108.80  
  Purchase #4 $125.48   13.705%   $142.677   $142.68   $142.70   $142.70  
  Purchase #5 $137.87   6.662%   $147.0549   $147.05   $147.05   $147.10  
  Purchase #6 $52.94   7.832%   $57.0863   $57.09   $57.10   $57.10  
  Purchase #7 $10.28   10.218%   $11.3304   $11.33   $11.35   $11.30  
  7 purchase totals = $603.57       $648.5095   $648.50   $648.55   $648.60