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 $181.32   3.388%   $187.4631   $187.46   $187.45   $187.50  
  Purchase #2 $182.66   5.871%   $193.384   $193.38   $193.40   $193.40  
  Purchase #3 $237.91   10.696%   $263.3569   $263.36   $263.35   $263.40  
  Purchase #4 $34.66   7.353%   $37.2085   $37.21   $37.20   $37.20  
  Purchase #5 $147.87   6.873%   $158.0331   $158.03   $158.05   $158.00  
  Purchase #6 $239.72   11.592%   $267.5083   $267.51   $267.50   $267.50  
  Purchase #7 $154.44   12.540%   $173.8068   $173.81   $173.80   $173.80  
  7 purchase totals = $1,178.58       $1,280.7607   $1,280.76   $1,280.75   $1,280.80