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 $53.49   4.564%   $55.9313   $55.93   $55.95   $55.90  
  Purchase #2 $39.35   13.497%   $44.6611   $44.66   $44.65   $44.70  
  Purchase #3 $176.39   11.701%   $197.0294   $197.03   $197.05   $197.00  
  Purchase #4 $54.37   5.489%   $57.3544   $57.35   $57.35   $57.40  
  Purchase #5 $183.76   9.462%   $201.1474   $201.15   $201.15   $201.10  
  Purchase #6 $10.99   13.678%   $12.4932   $12.49   $12.50   $12.50  
  Purchase #7 $250.81   3.200%   $258.8359   $258.84   $258.85   $258.80  
  7 purchase totals = $769.16       $827.4527   $827.45   $827.50   $827.40