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 $200.42   6.782%   $214.0125   $214.01   $214.00   $214.00  
  Purchase #2 $151.33   11.194%   $168.2699   $168.27   $168.25   $168.30  
  Purchase #3 $173.83   9.387%   $190.1474   $190.15   $190.15   $190.10  
  Purchase #4 $86.78   9.209%   $94.7716   $94.77   $94.75   $94.80  
  Purchase #5 $212.47   4.786%   $222.6388   $222.64   $222.65   $222.60  
  Purchase #6 $25.96   7.594%   $27.9314   $27.93   $27.95   $27.90  
  Purchase #7 $28.45   6.486%   $30.2953   $30.30   $30.30   $30.30  
  7 purchase totals = $879.24       $948.0669   $948.07   $948.05   $948.00