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 $101.26   13.591%   $115.0222   $115.02   $115.00   $115.00  
  Purchase #2 $207.26   10.417%   $228.8503   $228.85   $228.85   $228.90  
  Purchase #3 $73.63   6.581%   $78.4756   $78.48   $78.50   $78.50  
  Purchase #4 $144.28   10.253%   $159.073   $159.07   $159.05   $159.10  
  Purchase #5 $69.72   10.121%   $76.7764   $76.78   $76.80   $76.80  
  Purchase #6 $232.83   11.189%   $258.8813   $258.88   $258.90   $258.90  
  Purchase #7 $242.97   3.760%   $252.1057   $252.11   $252.10   $252.10  
  7 purchase totals = $1,071.95       $1,169.1845   $1,169.19   $1,169.20   $1,169.30