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 $183.30   12.233%   $205.7231   $205.72   $205.70   $205.70  
  Purchase #2 $229.57   9.172%   $250.6262   $250.63   $250.65   $250.60  
  Purchase #3 $195.90   13.473%   $222.2936   $222.29   $222.30   $222.30  
  Purchase #4 $45.91   5.662%   $48.5094   $48.51   $48.50   $48.50  
  Purchase #5 $51.83   7.305%   $55.6162   $55.62   $55.60   $55.60  
  Purchase #6 $143.75   6.299%   $152.8048   $152.80   $152.80   $152.80  
  Purchase #7 $21.49   10.728%   $23.7954   $23.80   $23.80   $23.80  
  7 purchase totals = $871.75       $959.3687   $959.37   $959.35   $959.30