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 $224.58   11.435%   $250.2607   $250.26   $250.25   $250.30  
  Purchase #2 $210.25   10.420%   $232.1581   $232.16   $232.15   $232.20  
  Purchase #3 $248.76   5.397%   $262.1856   $262.19   $262.20   $262.20  
  Purchase #4 $228.46   11.711%   $255.215   $255.22   $255.20   $255.20  
  Purchase #5 $31.73   10.627%   $35.1019   $35.10   $35.10   $35.10  
  Purchase #6 $244.34   3.286%   $252.369   $252.37   $252.35   $252.40  
  Purchase #7 $58.57   13.519%   $66.4881   $66.49   $66.50   $66.50  
  7 purchase totals = $1,246.69       $1,353.7784   $1,353.79   $1,353.75   $1,353.90