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 $61.69   5.508%   $65.0879   $65.09   $65.10   $65.10  
  Purchase #2 $40.50   7.827%   $43.6699   $43.67   $43.65   $43.70  
  Purchase #3 $213.95   7.449%   $229.8871   $229.89   $229.90   $229.90  
  Purchase #4 $190.52   6.492%   $202.8886   $202.89   $202.90   $202.90  
  Purchase #5 $151.93   10.853%   $168.419   $168.42   $168.40   $168.40  
  Purchase #6 $12.99   10.763%   $14.3881   $14.39   $14.40   $14.40  
  Purchase #7 $149.37   3.788%   $155.0281   $155.03   $155.05   $155.00  
  7 purchase totals = $820.95       $879.3687   $879.38   $879.40   $879.40