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 $207.71   13.402%   $235.5473   $235.55   $235.55   $235.50  
  Purchase #2 $38.42   11.858%   $42.9758   $42.98   $43.00   $43.00  
  Purchase #3 $88.93   8.866%   $96.8145   $96.81   $96.80   $96.80  
  Purchase #4 $120.33   11.778%   $134.5025   $134.50   $134.50   $134.50  
  Purchase #5 $179.53   8.710%   $195.1671   $195.17   $195.15   $195.20  
  Purchase #6 $120.87   12.489%   $135.9655   $135.97   $135.95   $136.00  
  Purchase #7 $168.95   10.354%   $186.4431   $186.44   $186.45   $186.40  
  7 purchase totals = $924.74       $1,027.4158   $1,027.42   $1,027.40   $1,027.40