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 $237.49   13.561%   $269.696   $269.70   $269.70   $269.70  
  Purchase #2 $46.37   5.730%   $49.027   $49.03   $49.05   $49.00  
  Purchase #3 $236.61   3.235%   $244.2643   $244.26   $244.25   $244.30  
  Purchase #4 $61.58   13.290%   $69.764   $69.76   $69.75   $69.80  
  Purchase #5 $186.89   10.840%   $207.1489   $207.15   $207.15   $207.10  
  Purchase #6 $63.89   13.375%   $72.4353   $72.44   $72.45   $72.40  
  Purchase #7 $41.56   4.306%   $43.3496   $43.35   $43.35   $43.30  
  7 purchase totals = $874.39       $955.6851   $955.69   $955.70   $955.60