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 $247.66   6.103%   $262.7747   $262.77   $262.75   $262.80  
  Purchase #2 $238.50   13.825%   $271.4726   $271.47   $271.45   $271.50  
  Purchase #3 $30.25   13.675%   $34.3867   $34.39   $34.40   $34.40  
  Purchase #4 $73.36   5.545%   $77.4278   $77.43   $77.45   $77.40  
  Purchase #5 $22.82   4.811%   $23.9179   $23.92   $23.90   $23.90  
  Purchase #6 $146.28   4.429%   $152.7587   $152.76   $152.75   $152.80  
  Purchase #7 $193.76   13.553%   $220.0203   $220.02   $220.00   $220.00  
  7 purchase totals = $952.63       $1,042.7587   $1,042.76   $1,042.70   $1,042.80