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 $23.61   7.814%   $25.4549   $25.45   $25.45   $25.50  
  Purchase #2 $207.80   10.358%   $229.3239   $229.32   $229.30   $229.30  
  Purchase #3 $51.68   7.710%   $55.6645   $55.66   $55.65   $55.70  
  Purchase #4 $61.33   7.148%   $65.7139   $65.71   $65.70   $65.70  
  Purchase #5 $42.34   12.257%   $47.5296   $47.53   $47.55   $47.50  
  Purchase #6 $194.93   6.814%   $208.2125   $208.21   $208.20   $208.20  
  Purchase #7 $170.47   6.847%   $182.1421   $182.14   $182.15   $182.10  
  7 purchase totals = $752.16       $814.0414   $814.02   $814.00   $814.00