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 $207.62   9.103%   $226.5196   $226.52   $226.50   $226.50  
  Purchase #2 $63.57   9.465%   $69.5869   $69.59   $69.60   $69.60  
  Purchase #3 $131.28   6.354%   $139.6215   $139.62   $139.60   $139.60  
  Purchase #4 $227.64   4.225%   $237.2578   $237.26   $237.25   $237.30  
  Purchase #5 $47.42   8.155%   $51.2871   $51.29   $51.30   $51.30  
  Purchase #6 $37.63   5.553%   $39.7196   $39.72   $39.70   $39.70  
  Purchase #7 $180.30   9.131%   $196.7632   $196.76   $196.75   $196.80  
  7 purchase totals = $895.46       $960.7557   $960.76   $960.70   $960.80