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 $240.28   9.121%   $262.1959   $262.20   $262.20   $262.20  
  Purchase #2 $211.48   9.430%   $231.4226   $231.42   $231.40   $231.40  
  Purchase #3 $246.79   4.529%   $257.9671   $257.97   $257.95   $258.00  
  Purchase #4 $82.54   4.503%   $86.2568   $86.26   $86.25   $86.30  
  Purchase #5 $249.35   8.243%   $269.9039   $269.90   $269.90   $269.90  
  Purchase #6 $205.44   4.239%   $214.1486   $214.15   $214.15   $214.10  
  Purchase #7 $169.61   3.786%   $176.0314   $176.03   $176.05   $176.00  
  7 purchase totals = $1,405.49       $1,497.9263   $1,497.93   $1,497.90   $1,497.90