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 $213.87   10.638%   $236.6215   $236.62   $236.60   $236.60  
  Purchase #2 $234.97   9.797%   $257.99   $257.99   $258.00   $258.00  
  Purchase #3 $101.92   12.667%   $114.8302   $114.83   $114.85   $114.80  
  Purchase #4 $19.91   13.566%   $22.611   $22.61   $22.60   $22.60  
  Purchase #5 $134.80   4.227%   $140.498   $140.50   $140.50   $140.50  
  Purchase #6 $239.46   8.818%   $260.5756   $260.58   $260.60   $260.60  
  Purchase #7 $38.55   13.582%   $43.7859   $43.79   $43.80   $43.80  
  7 purchase totals = $983.48       $1,076.9122   $1,076.92   $1,076.95   $1,076.90