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 $10.67   6.620%   $11.3764   $11.38   $11.40   $11.40  
  Purchase #2 $44.35   8.126%   $47.9539   $47.95   $47.95   $48.00  
  Purchase #3 $93.94   8.574%   $101.9944   $101.99   $102.00   $102.00  
  Purchase #4 $217.78   7.628%   $234.3923   $234.39   $234.40   $234.40  
  Purchase #5 $67.61   11.221%   $75.1965   $75.20   $75.20   $75.20  
  Purchase #6 $55.88   6.425%   $59.4703   $59.47   $59.45   $59.50  
  Purchase #7 $183.40   5.286%   $193.0945   $193.09   $193.10   $193.10  
  7 purchase totals = $673.63       $723.4783   $723.47   $723.50   $723.60