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 $24.27   9.587%   $26.5968   $26.60   $26.60   $26.60  
  Purchase #2 $88.72   11.707%   $99.1065   $99.11   $99.10   $99.10  
  Purchase #3 $199.99   8.678%   $217.3451   $217.35   $217.35   $217.30  
  Purchase #4 $246.61   11.476%   $274.911   $274.91   $274.90   $274.90  
  Purchase #5 $159.68   12.223%   $179.1977   $179.20   $179.20   $179.20  
  Purchase #6 $91.45   4.405%   $95.4784   $95.48   $95.50   $95.50  
  Purchase #7 $7.93   5.162%   $8.3393   $8.34   $8.35   $8.30  
  7 purchase totals = $818.65       $900.9748   $900.99   $901.00   $900.90