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 $238.80   9.701%   $261.966   $261.97   $261.95   $262.00  
  Purchase #2 $41.89   6.483%   $44.6057   $44.61   $44.60   $44.60  
  Purchase #3 $46.72   5.767%   $49.4143   $49.41   $49.40   $49.40  
  Purchase #4 $205.55   9.609%   $225.3013   $225.30   $225.30   $225.30  
  Purchase #5 $26.89   12.102%   $30.1442   $30.14   $30.15   $30.10  
  Purchase #6 $48.68   9.620%   $53.363   $53.36   $53.35   $53.40  
  Purchase #7 $196.46   8.756%   $213.662   $213.66   $213.65   $213.70  
  7 purchase totals = $804.99       $878.4565   $878.45   $878.40   $878.50