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 $24.96   5.177%   $26.2522   $26.25   $26.25   $26.30  
  Purchase #2 $50.42   9.768%   $55.345   $55.35   $55.35   $55.30  
  Purchase #3 $36.94   10.246%   $40.7249   $40.72   $40.70   $40.70  
  Purchase #4 $193.31   10.866%   $214.3151   $214.32   $214.30   $214.30  
  Purchase #5 $213.28   11.802%   $238.4513   $238.45   $238.45   $238.50  
  Purchase #6 $204.30   12.349%   $229.529   $229.53   $229.55   $229.50  
  Purchase #7 $156.77   13.575%   $178.0515   $178.05   $178.05   $178.10  
  7 purchase totals = $879.98       $982.6690   $982.67   $982.65   $982.70