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 $208.98   7.641%   $224.9482   $224.95   $224.95   $224.90  
  Purchase #2 $23.77   8.781%   $25.8572   $25.86   $25.85   $25.90  
  Purchase #3 $142.52   6.140%   $151.2707   $151.27   $151.25   $151.30  
  Purchase #4 $24.69   9.520%   $27.0405   $27.04   $27.05   $27.00  
  Purchase #5 $196.54   13.496%   $223.065   $223.07   $223.05   $223.10  
  Purchase #6 $174.98   9.494%   $191.5926   $191.59   $191.60   $191.60  
  Purchase #7 $50.26   11.837%   $56.2093   $56.21   $56.20   $56.20  
  7 purchase totals = $821.74       $899.9835   $899.99   $899.95   $900.00