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 $57.83   7.604%   $62.2274   $62.23   $62.25   $62.20  
  Purchase #2 $25.73   3.683%   $26.6776   $26.68   $26.70   $26.70  
  Purchase #3 $113.69   6.842%   $121.4687   $121.47   $121.45   $121.50  
  Purchase #4 $36.61   6.452%   $38.9721   $38.97   $38.95   $39.00  
  Purchase #5 $107.67   10.780%   $119.2768   $119.28   $119.30   $119.30  
  Purchase #6 $191.82   11.637%   $214.1421   $214.14   $214.15   $214.10  
  Purchase #7 $133.88   7.551%   $143.9893   $143.99   $144.00   $144.00  
  7 purchase totals = $667.23       $726.7540   $726.76   $726.80   $726.80