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 $122.95   13.513%   $139.5642   $139.56   $139.55   $139.60  
  Purchase #2 $214.88   11.601%   $239.8082   $239.81   $239.80   $239.80  
  Purchase #3 $48.33   9.863%   $53.0968   $53.10   $53.10   $53.10  
  Purchase #4 $115.27   5.206%   $121.271   $121.27   $121.25   $121.30  
  Purchase #5 $209.73   9.649%   $229.9668   $229.97   $229.95   $230.00  
  Purchase #6 $119.50   9.652%   $131.0341   $131.03   $131.05   $131.00  
  Purchase #7 $219.36   13.533%   $249.046   $249.05   $249.05   $249.00  
  7 purchase totals = $1,050.02       $1,163.7871   $1,163.79   $1,163.75   $1,163.80