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 $94.89   11.329%   $105.6401   $105.64   $105.65   $105.60  
  Purchase #2 $215.97   9.502%   $236.4915   $236.49   $236.50   $236.50  
  Purchase #3 $196.56   5.785%   $207.931   $207.93   $207.95   $207.90  
  Purchase #4 $40.42   4.844%   $42.3779   $42.38   $42.40   $42.40  
  Purchase #5 $68.93   8.409%   $74.7263   $74.73   $74.75   $74.70  
  Purchase #6 $86.50   5.874%   $91.581   $91.58   $91.60   $91.60  
  Purchase #7 $232.36   13.189%   $263.006   $263.01   $263.00   $263.00  
  7 purchase totals = $935.63       $1,021.7538   $1,021.76   $1,021.85   $1,021.70