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 $112.68   9.547%   $123.4376   $123.44   $123.45   $123.40  
  Purchase #2 $207.89   7.861%   $224.2322   $224.23   $224.25   $224.20  
  Purchase #3 $121.76   4.577%   $127.333   $127.33   $127.35   $127.30  
  Purchase #4 $48.53   10.711%   $53.728   $53.73   $53.75   $53.70  
  Purchase #5 $116.51   4.822%   $122.1281   $122.13   $122.15   $122.10  
  Purchase #6 $182.71   11.597%   $203.8989   $203.90   $203.90   $203.90  
  Purchase #7 $230.97   9.322%   $252.501   $252.50   $252.50   $252.50  
  7 purchase totals = $1,021.05       $1,107.2588   $1,107.26   $1,107.35   $1,107.10