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 $112.34   10.242%   $123.8459   $123.85   $123.85   $123.80  
  Purchase #2 $145.76   12.836%   $164.4698   $164.47   $164.45   $164.50  
  Purchase #3 $135.26   6.426%   $143.9518   $143.95   $143.95   $144.00  
  Purchase #4 $226.78   3.434%   $234.5676   $234.57   $234.55   $234.60  
  Purchase #5 $226.66   5.475%   $239.0696   $239.07   $239.05   $239.10  
  Purchase #6 $28.68   11.638%   $32.0178   $32.02   $32.00   $32.00  
  Purchase #7 $78.70   6.277%   $83.64   $83.64   $83.65   $83.60  
  7 purchase totals = $954.18       $1,021.5625   $1,021.57   $1,021.50   $1,021.60