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 $208.25   8.624%   $226.2095   $226.21   $226.20   $226.20  
  Purchase #2 $16.30   8.135%   $17.626   $17.63   $17.65   $17.60  
  Purchase #3 $195.95   13.301%   $222.0133   $222.01   $222.00   $222.00  
  Purchase #4 $93.78   10.504%   $103.6307   $103.63   $103.65   $103.60  
  Purchase #5 $158.90   7.463%   $170.7587   $170.76   $170.75   $170.80  
  Purchase #6 $129.83   3.685%   $134.6142   $134.61   $134.60   $134.60  
  Purchase #7 $27.60   5.783%   $29.1961   $29.20   $29.20   $29.20  
  7 purchase totals = $830.61       $904.0485   $904.05   $904.05   $904.00