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 $234.93   4.733%   $246.0492   $246.05   $246.05   $246.00  
  Purchase #2 $109.56   3.149%   $113.01   $113.01   $113.00   $113.00  
  Purchase #3 $17.34   11.273%   $19.2947   $19.29   $19.30   $19.30  
  Purchase #4 $203.64   5.357%   $214.549   $214.55   $214.55   $214.50  
  Purchase #5 $122.26   11.465%   $136.2771   $136.28   $136.30   $136.30  
  Purchase #6 $241.76   13.242%   $273.7739   $273.77   $273.75   $273.80  
  Purchase #7 $199.50   8.652%   $216.7607   $216.76   $216.75   $216.80  
  7 purchase totals = $1,128.99       $1,219.7146   $1,219.71   $1,219.70   $1,219.70