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 $225.68   8.387%   $244.6078   $244.61   $244.60   $244.60  
  Purchase #2 $136.79   5.591%   $144.4379   $144.44   $144.45   $144.40  
  Purchase #3 $35.36   6.322%   $37.5955   $37.60   $37.60   $37.60  
  Purchase #4 $83.45   4.523%   $87.2244   $87.22   $87.20   $87.20  
  Purchase #5 $225.26   9.597%   $246.8782   $246.88   $246.90   $246.90  
  Purchase #6 $115.25   7.241%   $123.5953   $123.60   $123.60   $123.60  
  Purchase #7 $44.77   9.574%   $49.0563   $49.06   $49.05   $49.10  
  7 purchase totals = $866.56       $933.3954   $933.41   $933.40   $933.40