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 $112.71   10.573%   $124.6268   $124.63   $124.65   $124.60  
  Purchase #2 $199.39   13.517%   $226.3415   $226.34   $226.35   $226.30  
  Purchase #3 $214.25   10.128%   $235.9492   $235.95   $235.95   $235.90  
  Purchase #4 $32.39   7.311%   $34.758   $34.76   $34.75   $34.80  
  Purchase #5 $27.70   4.428%   $28.9266   $28.93   $28.95   $28.90  
  Purchase #6 $230.97   4.846%   $242.1628   $242.16   $242.15   $242.20  
  Purchase #7 $240.87   11.321%   $268.1389   $268.14   $268.15   $268.10  
  7 purchase totals = $1,058.28       $1,160.9038   $1,160.91   $1,160.95   $1,160.80