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 $218.90   9.187%   $239.0103   $239.01   $239.00   $239.00  
  Purchase #2 $139.45   9.504%   $152.7033   $152.70   $152.70   $152.70  
  Purchase #3 $121.37   10.660%   $134.308   $134.31   $134.30   $134.30  
  Purchase #4 $68.87   7.724%   $74.1895   $74.19   $74.20   $74.20  
  Purchase #5 $144.77   5.384%   $152.5644   $152.56   $152.55   $152.60  
  Purchase #6 $27.60   11.370%   $30.7381   $30.74   $30.75   $30.70  
  Purchase #7 $105.79   5.377%   $111.4783   $111.48   $111.50   $111.50  
  7 purchase totals = $826.75       $894.9919   $894.99   $895.00   $895.00