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 $61.83   3.478%   $63.9804   $63.98   $64.00   $64.00  
  Purchase #2 $122.69   4.169%   $127.8049   $127.80   $127.80   $127.80  
  Purchase #3 $168.75   8.380%   $182.8913   $182.89   $182.90   $182.90  
  Purchase #4 $37.66   3.822%   $39.0994   $39.10   $39.10   $39.10  
  Purchase #5 $224.73   11.258%   $250.0301   $250.03   $250.05   $250.00  
  Purchase #6 $172.88   12.403%   $194.3223   $194.32   $194.30   $194.30  
  Purchase #7 $26.54   12.246%   $29.7901   $29.79   $29.80   $29.80  
  7 purchase totals = $815.08       $887.9185   $887.91   $887.95   $887.90