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 $236.55   12.113%   $265.2033   $265.20   $265.20   $265.20  
  Purchase #2 $173.80   9.227%   $189.8365   $189.84   $189.85   $189.80  
  Purchase #3 $175.85   8.437%   $190.6865   $190.69   $190.70   $190.70  
  Purchase #4 $113.52   11.350%   $126.4045   $126.40   $126.40   $126.40  
  Purchase #5 $136.93   11.765%   $153.0398   $153.04   $153.05   $153.00  
  Purchase #6 $179.61   11.681%   $200.5902   $200.59   $200.60   $200.60  
  Purchase #7 $102.80   11.687%   $114.8142   $114.81   $114.80   $114.80  
  7 purchase totals = $1,119.06       $1,240.5750   $1,240.57   $1,240.60   $1,240.50