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 $56.51   10.344%   $62.3554   $62.36   $62.35   $62.40  
  Purchase #2 $48.92   13.768%   $55.6553   $55.66   $55.65   $55.70  
  Purchase #3 $16.99   8.167%   $18.3776   $18.38   $18.40   $18.40  
  Purchase #4 $181.58   7.614%   $195.4055   $195.41   $195.40   $195.40  
  Purchase #5 $81.41   6.326%   $86.56   $86.56   $86.55   $86.60  
  Purchase #6 $189.86   13.271%   $215.0563   $215.06   $215.05   $215.10  
  Purchase #7 $237.93   9.486%   $260.5   $260.50   $260.50   $260.50  
  7 purchase totals = $813.20       $893.9101   $893.93   $893.90   $894.10