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 $25.98   3.752%   $26.9548   $26.95   $26.95   $27.00  
  Purchase #2 $73.37   9.274%   $80.1743   $80.17   $80.15   $80.20  
  Purchase #3 $200.30   4.174%   $208.6605   $208.66   $208.65   $208.70  
  Purchase #4 $216.89   9.864%   $238.284   $238.28   $238.30   $238.30  
  Purchase #5 $250.62   12.803%   $282.7069   $282.71   $282.70   $282.70  
  Purchase #6 $56.66   6.368%   $60.2681   $60.27   $60.25   $60.30  
  Purchase #7 $99.70   8.839%   $108.5125   $108.51   $108.50   $108.50  
  7 purchase totals = $923.52       $1,005.5611   $1,005.55   $1,005.50   $1,005.70