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 $39.92   11.843%   $44.6477   $44.65   $44.65   $44.60  
  Purchase #2 $171.57   12.783%   $193.5018   $193.50   $193.50   $193.50  
  Purchase #3 $63.48   6.258%   $67.4526   $67.45   $67.45   $67.50  
  Purchase #4 $50.70   12.235%   $56.9031   $56.90   $56.90   $56.90  
  Purchase #5 $170.99   9.171%   $186.6715   $186.67   $186.65   $186.70  
  Purchase #6 $182.46   10.158%   $200.9943   $200.99   $201.00   $201.00  
  Purchase #7 $49.55   3.105%   $51.0885   $51.09   $51.10   $51.10  
  7 purchase totals = $728.67       $801.2595   $801.25   $801.25   $801.30