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 $236.70   11.488%   $263.8921   $263.89   $263.90   $263.90  
  Purchase #2 $24.45   8.661%   $26.5676   $26.57   $26.55   $26.60  
  Purchase #3 $143.61   10.692%   $158.9648   $158.96   $158.95   $159.00  
  Purchase #4 $17.35   4.782%   $18.1797   $18.18   $18.20   $18.20  
  Purchase #5 $221.63   6.752%   $236.5945   $236.59   $236.60   $236.60  
  Purchase #6 $116.67   13.775%   $132.7413   $132.74   $132.75   $132.70  
  Purchase #7 $173.99   7.278%   $186.653   $186.65   $186.65   $186.70  
  7 purchase totals = $934.40       $1,023.5930   $1,023.58   $1,023.60   $1,023.70