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 $228.99   11.791%   $255.9902   $255.99   $256.00   $256.00  
  Purchase #2 $221.65   12.622%   $249.6267   $249.63   $249.65   $249.60  
  Purchase #3 $52.63   8.139%   $56.9136   $56.91   $56.90   $56.90  
  Purchase #4 $67.55   3.133%   $69.6663   $69.67   $69.65   $69.70  
  Purchase #5 $70.67   4.125%   $73.5851   $73.59   $73.60   $73.60  
  Purchase #6 $56.69   6.737%   $60.5092   $60.51   $60.50   $60.50  
  Purchase #7 $219.75   4.210%   $229.0015   $229.00   $229.00   $229.00  
  7 purchase totals = $917.93       $995.2926   $995.30   $995.30   $995.30