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 $240.81   11.376%   $268.2045   $268.20   $268.20   $268.20  
  Purchase #2 $133.37   10.486%   $147.3552   $147.36   $147.35   $147.40  
  Purchase #3 $85.63   4.531%   $89.5099   $89.51   $89.50   $89.50  
  Purchase #4 $129.28   5.869%   $136.8674   $136.87   $136.85   $136.90  
  Purchase #5 $10.75   6.428%   $11.441   $11.44   $11.45   $11.40  
  Purchase #6 $210.83   7.322%   $226.267   $226.27   $226.25   $226.30  
  Purchase #7 $35.88   12.157%   $40.2419   $40.24   $40.25   $40.20  
  7 purchase totals = $846.55       $919.8869   $919.89   $919.85   $919.90