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 $213.68   13.189%   $241.8623   $241.86   $241.85   $241.90  
  Purchase #2 $126.26   10.501%   $139.5186   $139.52   $139.50   $139.50  
  Purchase #3 $113.49   8.747%   $123.417   $123.42   $123.40   $123.40  
  Purchase #4 $22.73   3.393%   $23.5012   $23.50   $23.50   $23.50  
  Purchase #5 $201.99   6.649%   $215.4203   $215.42   $215.40   $215.40  
  Purchase #6 $9.49   4.867%   $9.9519   $9.95   $9.95   $10.00  
  Purchase #7 $21.98   5.328%   $23.1511   $23.15   $23.15   $23.20  
  7 purchase totals = $709.62       $776.8224   $776.82   $776.75   $776.90