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 $61.38   4.859%   $64.3625   $64.36   $64.35   $64.40  
  Purchase #2 $196.75   7.653%   $211.8073   $211.81   $211.80   $211.80  
  Purchase #3 $134.40   5.827%   $142.2315   $142.23   $142.25   $142.20  
  Purchase #4 $76.89   4.565%   $80.4   $80.40   $80.40   $80.40  
  Purchase #5 $241.65   8.361%   $261.8544   $261.85   $261.85   $261.90  
  Purchase #6 $177.27   9.717%   $194.4953   $194.50   $194.50   $194.50  
  Purchase #7 $179.57   4.217%   $187.1425   $187.14   $187.15   $187.10  
  7 purchase totals = $1,067.91       $1,142.2935   $1,142.29   $1,142.30   $1,142.30