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 $13.54   12.559%   $15.2405   $15.24   $15.25   $15.20  
  Purchase #2 $105.36   12.339%   $118.3604   $118.36   $118.35   $118.40  
  Purchase #3 $158.32   10.389%   $174.7679   $174.77   $174.75   $174.80  
  Purchase #4 $107.97   13.517%   $122.5643   $122.56   $122.55   $122.60  
  Purchase #5 $180.76   5.326%   $190.3873   $190.39   $190.40   $190.40  
  Purchase #6 $98.28   3.433%   $101.654   $101.65   $101.65   $101.70  
  Purchase #7 $177.74   13.610%   $201.9304   $201.93   $201.95   $201.90  
  7 purchase totals = $841.97       $924.9048   $924.90   $924.90   $925.00