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 $121.72   11.641%   $135.8894   $135.89   $135.90   $135.90  
  Purchase #2 $245.90   8.851%   $267.6646   $267.66   $267.65   $267.70  
  Purchase #3 $213.50   5.858%   $226.0068   $226.01   $226.00   $226.00  
  Purchase #4 $43.43   12.823%   $48.999   $49.00   $49.00   $49.00  
  Purchase #5 $217.64   10.153%   $239.737   $239.74   $239.75   $239.70  
  Purchase #6 $23.36   11.534%   $26.0543   $26.05   $26.05   $26.10  
  Purchase #7 $46.49   8.173%   $50.2896   $50.29   $50.30   $50.30  
  7 purchase totals = $912.04       $994.6407   $994.64   $994.65   $994.70