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 $24.51   8.803%   $26.6676   $26.67   $26.65   $26.70  
  Purchase #2 $224.94   10.238%   $247.9694   $247.97   $247.95   $248.00  
  Purchase #3 $154.63   6.719%   $165.0196   $165.02   $165.00   $165.00  
  Purchase #4 $8.91   5.865%   $9.4326   $9.43   $9.45   $9.40  
  Purchase #5 $241.26   5.730%   $255.0842   $255.08   $255.10   $255.10  
  Purchase #6 $166.25   11.835%   $185.9257   $185.93   $185.95   $185.90  
  Purchase #7 $52.99   9.397%   $57.9695   $57.97   $57.95   $58.00  
  7 purchase totals = $873.49       $948.0686   $948.07   $948.05   $948.10