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 $67.80   8.591%   $73.6247   $73.62   $73.60   $73.60  
  Purchase #2 $54.39   10.589%   $60.1494   $60.15   $60.15   $60.10  
  Purchase #3 $22.78   13.801%   $25.9239   $25.92   $25.90   $25.90  
  Purchase #4 $118.43   13.439%   $134.3458   $134.35   $134.35   $134.30  
  Purchase #5 $199.44   4.287%   $207.99   $207.99   $208.00   $208.00  
  Purchase #6 $8.39   11.443%   $9.3501   $9.35   $9.35   $9.40  
  Purchase #7 $117.54   4.678%   $123.0385   $123.04   $123.05   $123.00  
  7 purchase totals = $588.77       $634.4224   $634.42   $634.40   $634.30