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 $23.48   11.739%   $26.2363   $26.24   $26.25   $26.20  
  Purchase #2 $164.65   8.409%   $178.4954   $178.50   $178.50   $178.50  
  Purchase #3 $30.26   7.196%   $32.4375   $32.44   $32.45   $32.40  
  Purchase #4 $95.33   12.391%   $107.1423   $107.14   $107.15   $107.10  
  Purchase #5 $115.25   5.857%   $122.0002   $122.00   $122.00   $122.00  
  Purchase #6 $46.40   8.143%   $50.1784   $50.18   $50.20   $50.20  
  Purchase #7 $6.90   11.831%   $7.7163   $7.72   $7.70   $7.70  
  7 purchase totals = $482.27       $524.2064   $524.22   $524.25   $524.10