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 $214.75   13.652%   $244.0677   $244.07   $244.05   $244.10  
  Purchase #2 $186.63   3.652%   $193.4457   $193.45   $193.45   $193.40  
  Purchase #3 $23.56   13.539%   $26.7498   $26.75   $26.75   $26.70  
  Purchase #4 $98.67   3.340%   $101.9656   $101.97   $101.95   $102.00  
  Purchase #5 $208.48   3.179%   $215.1076   $215.11   $215.10   $215.10  
  Purchase #6 $114.58   8.664%   $124.5072   $124.51   $124.50   $124.50  
  Purchase #7 $11.36   6.736%   $12.1252   $12.13   $12.15   $12.10  
  7 purchase totals = $858.03       $917.9688   $917.99   $917.95   $917.90