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 $243.87   9.301%   $266.5523   $266.55   $266.55   $266.60  
  Purchase #2 $113.53   3.282%   $117.2561   $117.26   $117.25   $117.30  
  Purchase #3 $44.82   8.127%   $48.4625   $48.46   $48.45   $48.50  
  Purchase #4 $156.76   11.839%   $175.3188   $175.32   $175.30   $175.30  
  Purchase #5 $240.50   4.181%   $250.5553   $250.56   $250.55   $250.60  
  Purchase #6 $97.42   11.699%   $108.8172   $108.82   $108.80   $108.80  
  Purchase #7 $55.81   3.138%   $57.5613   $57.56   $57.55   $57.60  
  7 purchase totals = $952.71       $1,024.5235   $1,024.53   $1,024.45   $1,024.70