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 $24.28   8.116%   $26.2506   $26.25   $26.25   $26.30  
  Purchase #2 $223.90   4.293%   $233.512   $233.51   $233.50   $233.50  
  Purchase #3 $103.65   13.647%   $117.7951   $117.80   $117.80   $117.80  
  Purchase #4 $215.51   11.826%   $240.9962   $241.00   $241.00   $241.00  
  Purchase #5 $152.29   9.202%   $166.3037   $166.30   $166.30   $166.30  
  Purchase #6 $248.96   4.838%   $261.0047   $261.00   $261.00   $261.00  
  Purchase #7 $241.97   7.422%   $259.929   $259.93   $259.95   $259.90  
  7 purchase totals = $1,210.56       $1,305.7913   $1,305.79   $1,305.80   $1,305.80