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 $63.60   8.727%   $69.1504   $69.15   $69.15   $69.20  
  Purchase #2 $244.49   11.788%   $273.3105   $273.31   $273.30   $273.30  
  Purchase #3 $83.58   5.274%   $87.988   $87.99   $88.00   $88.00  
  Purchase #4 $140.73   5.528%   $148.5096   $148.51   $148.50   $148.50  
  Purchase #5 $224.78   13.712%   $255.6018   $255.60   $255.60   $255.60  
  Purchase #6 $111.69   6.845%   $119.3352   $119.34   $119.35   $119.30  
  Purchase #7 $66.69   11.767%   $74.5374   $74.54   $74.55   $74.50  
  7 purchase totals = $935.56       $1,028.4329   $1,028.44   $1,028.45   $1,028.40