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 $239.51   7.721%   $258.0026   $258.00   $258.00   $258.00  
  Purchase #2 $8.38   3.169%   $8.6456   $8.65   $8.65   $8.60  
  Purchase #3 $51.66   11.316%   $57.5058   $57.51   $57.50   $57.50  
  Purchase #4 $213.27   11.191%   $237.137   $237.14   $237.15   $237.10  
  Purchase #5 $158.83   7.737%   $171.1187   $171.12   $171.10   $171.10  
  Purchase #6 $227.29   8.418%   $246.4233   $246.42   $246.40   $246.40  
  Purchase #7 $55.49   4.581%   $58.032   $58.03   $58.05   $58.00  
  7 purchase totals = $954.43       $1,036.8650   $1,036.87   $1,036.85   $1,036.70