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 $62.99   5.745%   $66.6088   $66.61   $66.60   $66.60  
  Purchase #2 $249.46   3.424%   $258.0015   $258.00   $258.00   $258.00  
  Purchase #3 $94.80   4.599%   $99.1599   $99.16   $99.15   $99.20  
  Purchase #4 $30.77   9.455%   $33.6793   $33.68   $33.70   $33.70  
  Purchase #5 $98.92   7.571%   $106.4092   $106.41   $106.40   $106.40  
  Purchase #6 $215.48   4.735%   $225.683   $225.68   $225.70   $225.70  
  Purchase #7 $117.85   10.367%   $130.0675   $130.07   $130.05   $130.10  
  7 purchase totals = $870.27       $919.6092   $919.61   $919.60   $919.70