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 $61.77   13.331%   $70.0046   $70.00   $70.00   $70.00  
  Purchase #2 $250.75   4.102%   $261.0358   $261.04   $261.05   $261.00  
  Purchase #3 $212.40   9.269%   $232.0874   $232.09   $232.10   $232.10  
  Purchase #4 $110.57   13.176%   $125.1387   $125.14   $125.15   $125.10  
  Purchase #5 $76.57   4.834%   $80.2714   $80.27   $80.25   $80.30  
  Purchase #6 $24.61   9.599%   $26.9723   $26.97   $26.95   $27.00  
  Purchase #7 $95.45   13.657%   $108.4856   $108.49   $108.50   $108.50  
  7 purchase totals = $832.12       $903.9958   $904.00   $904.00   $904.00