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 $84.92   11.623%   $94.7903   $94.79   $94.80   $94.80  
  Purchase #2 $94.82   11.233%   $105.4711   $105.47   $105.45   $105.50  
  Purchase #3 $58.25   8.399%   $63.1424   $63.14   $63.15   $63.10  
  Purchase #4 $214.35   12.859%   $241.9133   $241.91   $241.90   $241.90  
  Purchase #5 $199.32   4.313%   $207.9167   $207.92   $207.90   $207.90  
  Purchase #6 $176.49   7.809%   $190.2721   $190.27   $190.25   $190.30  
  Purchase #7 $53.87   13.348%   $61.0606   $61.06   $61.05   $61.10  
  7 purchase totals = $882.02       $964.5665   $964.56   $964.50   $964.60