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 $54.70   12.569%   $61.5752   $61.58   $61.60   $61.60  
  Purchase #2 $43.53   13.661%   $49.4766   $49.48   $49.50   $49.50  
  Purchase #3 $106.50   8.853%   $115.9284   $115.93   $115.95   $115.90  
  Purchase #4 $38.85   4.595%   $40.6352   $40.64   $40.65   $40.60  
  Purchase #5 $170.39   13.554%   $193.4847   $193.48   $193.50   $193.50  
  Purchase #6 $241.52   7.128%   $258.7355   $258.74   $258.75   $258.70  
  Purchase #7 $69.42   13.271%   $78.6327   $78.63   $78.65   $78.60  
  7 purchase totals = $724.91       $798.4683   $798.48   $798.60   $798.40