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 $208.86   8.764%   $227.1645   $227.16   $227.15   $227.20  
  Purchase #2 $175.61   5.302%   $184.9208   $184.92   $184.90   $184.90  
  Purchase #3 $78.40   5.288%   $82.5458   $82.55   $82.55   $82.50  
  Purchase #4 $125.94   4.562%   $131.6854   $131.69   $131.70   $131.70  
  Purchase #5 $208.33   9.670%   $228.4755   $228.48   $228.50   $228.50  
  Purchase #6 $67.36   8.351%   $72.9852   $72.99   $73.00   $73.00  
  Purchase #7 $215.91   12.179%   $242.2057   $242.21   $242.20   $242.20  
  7 purchase totals = $1,080.41       $1,169.9829   $1,170.00   $1,170.00   $1,170.00