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 $41.51   5.463%   $43.7777   $43.78   $43.80   $43.80  
  Purchase #2 $110.58   3.296%   $114.2247   $114.22   $114.20   $114.20  
  Purchase #3 $44.61   12.136%   $50.0239   $50.02   $50.00   $50.00  
  Purchase #4 $233.31   8.594%   $253.3607   $253.36   $253.35   $253.40  
  Purchase #5 $17.50   12.722%   $19.7264   $19.73   $19.75   $19.70  
  Purchase #6 $246.25   8.705%   $267.6861   $267.69   $267.70   $267.70  
  Purchase #7 $223.93   5.382%   $235.9819   $235.98   $236.00   $236.00  
  7 purchase totals = $917.69       $984.7814   $984.78   $984.80   $984.80