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 $23.49   12.759%   $26.4871   $26.49   $26.50   $26.50  
  Purchase #2 $13.32   9.332%   $14.563   $14.56   $14.55   $14.60  
  Purchase #3 $119.70   13.524%   $135.8882   $135.89   $135.90   $135.90  
  Purchase #4 $194.68   6.299%   $206.9429   $206.94   $206.95   $206.90  
  Purchase #5 $245.51   13.679%   $279.0933   $279.09   $279.10   $279.10  
  Purchase #6 $179.95   7.435%   $193.3293   $193.33   $193.35   $193.30  
  Purchase #7 $9.39   5.852%   $9.9395   $9.94   $9.95   $9.90  
  7 purchase totals = $786.04       $866.2433   $866.24   $866.30   $866.20