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 $60.36   13.237%   $68.3499   $68.35   $68.35   $68.30  
  Purchase #2 $115.72   3.339%   $119.5839   $119.58   $119.60   $119.60  
  Purchase #3 $117.32   7.569%   $126.2   $126.20   $126.20   $126.20  
  Purchase #4 $53.75   8.733%   $58.444   $58.44   $58.45   $58.40  
  Purchase #5 $40.74   7.849%   $43.9377   $43.94   $43.95   $43.90  
  Purchase #6 $149.38   10.391%   $164.9021   $164.90   $164.90   $164.90  
  Purchase #7 $60.90   12.854%   $68.7281   $68.73   $68.75   $68.70  
  7 purchase totals = $598.17       $650.1457   $650.14   $650.20   $650.00