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 $224.79   11.539%   $250.7285   $250.73   $250.75   $250.70  
  Purchase #2 $195.38   8.379%   $211.7509   $211.75   $211.75   $211.80  
  Purchase #3 $6.50   6.417%   $6.9171   $6.92   $6.90   $6.90  
  Purchase #4 $59.30   12.224%   $66.5488   $66.55   $66.55   $66.50  
  Purchase #5 $41.70   5.687%   $44.0715   $44.07   $44.05   $44.10  
  Purchase #6 $38.38   10.151%   $42.276   $42.28   $42.30   $42.30  
  Purchase #7 $185.87   4.126%   $193.539   $193.54   $193.55   $193.50  
  7 purchase totals = $751.92       $815.8318   $815.84   $815.85   $815.80