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 $55.87   9.773%   $61.3302   $61.33   $61.35   $61.30  
  Purchase #2 $30.49   9.537%   $33.3978   $33.40   $33.40   $33.40  
  Purchase #3 $136.75   7.176%   $146.5632   $146.56   $146.55   $146.60  
  Purchase #4 $61.99   5.119%   $65.1633   $65.16   $65.15   $65.20  
  Purchase #5 $130.83   8.816%   $142.364   $142.36   $142.35   $142.40  
  Purchase #6 $33.74   9.408%   $36.9143   $36.91   $36.90   $36.90  
  Purchase #7 $113.82   7.225%   $122.0435   $122.04   $122.05   $122.00  
  7 purchase totals = $563.49       $607.7763   $607.76   $607.75   $607.80