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 $24.33   9.194%   $26.5669   $26.57   $26.55   $26.60  
  Purchase #2 $41.45   6.721%   $44.2359   $44.24   $44.25   $44.20  
  Purchase #3 $10.26   13.593%   $11.6546   $11.65   $11.65   $11.70  
  Purchase #4 $195.54   4.719%   $204.7675   $204.77   $204.75   $204.80  
  Purchase #5 $157.48   10.484%   $173.9902   $173.99   $174.00   $174.00  
  Purchase #6 $233.29   6.284%   $247.9499   $247.95   $247.95   $247.90  
  Purchase #7 $114.64   8.817%   $124.7478   $124.75   $124.75   $124.70  
  7 purchase totals = $776.99       $833.9128   $833.92   $833.90   $833.90