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 $231.81   10.630%   $256.4514   $256.45   $256.45   $256.50  
  Purchase #2 $18.89   6.375%   $20.0942   $20.09   $20.10   $20.10  
  Purchase #3 $7.62   10.680%   $8.4338   $8.43   $8.45   $8.40  
  Purchase #4 $222.64   6.482%   $237.0715   $237.07   $237.05   $237.10  
  Purchase #5 $138.50   13.849%   $157.6809   $157.68   $157.70   $157.70  
  Purchase #6 $37.48   13.860%   $42.6747   $42.67   $42.65   $42.70  
  Purchase #7 $158.53   12.655%   $178.592   $178.59   $178.60   $178.60  
  7 purchase totals = $815.47       $900.9985   $900.98   $901.00   $901.10