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 $183.50   11.734%   $205.0319   $205.03   $205.05   $205.00  
  Purchase #2 $22.41   4.735%   $23.4711   $23.47   $23.45   $23.50  
  Purchase #3 $117.42   13.738%   $133.5512   $133.55   $133.55   $133.60  
  Purchase #4 $200.85   3.660%   $208.2011   $208.20   $208.20   $208.20  
  Purchase #5 $72.75   9.357%   $79.5572   $79.56   $79.55   $79.60  
  Purchase #6 $244.50   12.166%   $274.2459   $274.25   $274.25   $274.20  
  Purchase #7 $232.96   8.261%   $252.2048   $252.20   $252.20   $252.20  
  7 purchase totals = $1,074.39       $1,176.2632   $1,176.26   $1,176.25   $1,176.30