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 $51.54   11.850%   $57.6475   $57.65   $57.65   $57.60  
  Purchase #2 $200.39   13.242%   $226.9256   $226.93   $226.95   $226.90  
  Purchase #3 $177.69   3.357%   $183.6551   $183.66   $183.65   $183.70  
  Purchase #4 $94.69   4.425%   $98.88   $98.88   $98.90   $98.90  
  Purchase #5 $69.39   10.848%   $76.9174   $76.92   $76.90   $76.90  
  Purchase #6 $77.85   8.538%   $84.4968   $84.50   $84.50   $84.50  
  Purchase #7 $69.51   8.754%   $75.5949   $75.59   $75.60   $75.60  
  7 purchase totals = $741.06       $804.1173   $804.13   $804.15   $804.10