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 $199.72   4.484%   $208.6754   $208.68   $208.70   $208.70  
  Purchase #2 $249.96   6.152%   $265.3375   $265.34   $265.35   $265.30  
  Purchase #3 $245.46   13.601%   $278.845   $278.85   $278.85   $278.80  
  Purchase #4 $46.58   7.310%   $49.985   $49.99   $50.00   $50.00  
  Purchase #5 $119.92   6.431%   $127.6321   $127.63   $127.65   $127.60  
  Purchase #6 $214.83   4.552%   $224.6091   $224.61   $224.60   $224.60  
  Purchase #7 $215.69   7.119%   $231.045   $231.05   $231.05   $231.00  
  7 purchase totals = $1,292.16       $1,386.1291   $1,386.15   $1,386.20   $1,386.00