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 $215.49   9.351%   $235.6405   $235.64   $235.65   $235.60  
  Purchase #2 $241.50   7.637%   $259.9434   $259.94   $259.95   $259.90  
  Purchase #3 $44.46   10.695%   $49.215   $49.22   $49.20   $49.20  
  Purchase #4 $201.44   6.696%   $214.9284   $214.93   $214.95   $214.90  
  Purchase #5 $183.30   7.431%   $196.921   $196.92   $196.90   $196.90  
  Purchase #6 $157.42   12.309%   $176.7968   $176.80   $176.80   $176.80  
  Purchase #7 $190.34   8.777%   $207.0461   $207.05   $207.05   $207.00  
  7 purchase totals = $1,233.95       $1,340.4912   $1,340.50   $1,340.50   $1,340.30