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 $185.32   12.688%   $208.8334   $208.83   $208.85   $208.80  
  Purchase #2 $248.54   4.633%   $260.0549   $260.05   $260.05   $260.10  
  Purchase #3 $211.78   11.535%   $236.2088   $236.21   $236.20   $236.20  
  Purchase #4 $81.45   5.766%   $86.1464   $86.15   $86.15   $86.10  
  Purchase #5 $75.34   9.386%   $82.4114   $82.41   $82.40   $82.40  
  Purchase #6 $206.96   3.846%   $214.9197   $214.92   $214.90   $214.90  
  Purchase #7 $66.64   12.181%   $74.7574   $74.76   $74.75   $74.80  
  7 purchase totals = $1,076.03       $1,163.3320   $1,163.33   $1,163.30   $1,163.30