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 $211.94   9.499%   $232.0722   $232.07   $232.05   $232.10  
  Purchase #2 $50.79   11.652%   $56.7081   $56.71   $56.70   $56.70  
  Purchase #3 $54.76   6.465%   $58.3002   $58.30   $58.30   $58.30  
  Purchase #4 $226.73   5.776%   $239.8259   $239.83   $239.85   $239.80  
  Purchase #5 $197.63   4.511%   $206.5451   $206.55   $206.55   $206.50  
  Purchase #6 $164.69   13.458%   $186.854   $186.85   $186.85   $186.90  
  Purchase #7 $236.95   10.645%   $262.1733   $262.17   $262.15   $262.20  
  7 purchase totals = $1,143.49       $1,242.4788   $1,242.48   $1,242.45   $1,242.50