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 $233.81   6.522%   $249.0591   $249.06   $249.05   $249.10  
  Purchase #2 $128.26   11.435%   $142.9265   $142.93   $142.95   $142.90  
  Purchase #3 $162.93   6.294%   $173.1848   $173.18   $173.20   $173.20  
  Purchase #4 $95.47   3.383%   $98.6998   $98.70   $98.70   $98.70  
  Purchase #5 $192.64   9.209%   $210.3802   $210.38   $210.40   $210.40  
  Purchase #6 $24.48   11.597%   $27.3189   $27.32   $27.30   $27.30  
  Purchase #7 $119.92   12.151%   $134.4915   $134.49   $134.50   $134.50  
  7 purchase totals = $957.51       $1,036.0608   $1,036.06   $1,036.10   $1,036.10