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 $76.61   7.526%   $82.3757   $82.38   $82.40   $82.40  
  Purchase #2 $185.68   4.333%   $193.7255   $193.73   $193.75   $193.70  
  Purchase #3 $67.95   9.832%   $74.6308   $74.63   $74.65   $74.60  
  Purchase #4 $224.87   10.662%   $248.8456   $248.85   $248.85   $248.80  
  Purchase #5 $164.27   13.769%   $186.8883   $186.89   $186.90   $186.90  
  Purchase #6 $93.70   11.192%   $104.1869   $104.19   $104.20   $104.20  
  Purchase #7 $30.31   7.664%   $32.633   $32.63   $32.65   $32.60  
  7 purchase totals = $843.39       $923.2858   $923.30   $923.40   $923.20