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 $47.97   12.651%   $54.0387   $54.04   $54.05   $54.00  
  Purchase #2 $87.52   10.119%   $96.3761   $96.38   $96.40   $96.40  
  Purchase #3 $15.28   11.212%   $16.9932   $16.99   $17.00   $17.00  
  Purchase #4 $151.32   3.182%   $156.135   $156.14   $156.15   $156.10  
  Purchase #5 $180.49   12.159%   $202.4358   $202.44   $202.45   $202.40  
  Purchase #6 $131.76   8.490%   $142.9464   $142.95   $142.95   $142.90  
  Purchase #7 $221.73   6.616%   $236.3997   $236.40   $236.40   $236.40  
  7 purchase totals = $836.07       $905.3249   $905.34   $905.40   $905.20