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 $54.59   7.146%   $58.491   $58.49   $58.50   $58.50  
  Purchase #2 $85.79   5.577%   $90.5745   $90.57   $90.55   $90.60  
  Purchase #3 $83.41   11.673%   $93.1464   $93.15   $93.15   $93.10  
  Purchase #4 $222.65   6.277%   $236.6257   $236.63   $236.65   $236.60  
  Purchase #5 $49.28   9.765%   $54.0922   $54.09   $54.10   $54.10  
  Purchase #6 $177.62   6.369%   $188.9326   $188.93   $188.95   $188.90  
  Purchase #7 $207.99   7.794%   $224.2007   $224.20   $224.20   $224.20  
  7 purchase totals = $881.33       $946.0631   $946.06   $946.10   $946.00