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 $64.81   12.318%   $72.7933   $72.79   $72.80   $72.80  
  Purchase #2 $192.94   11.563%   $215.2497   $215.25   $215.25   $215.20  
  Purchase #3 $248.64   13.526%   $282.271   $282.27   $282.25   $282.30  
  Purchase #4 $230.27   3.259%   $237.7745   $237.77   $237.75   $237.80  
  Purchase #5 $243.72   4.300%   $254.2   $254.20   $254.20   $254.20  
  Purchase #6 $47.71   8.451%   $51.742   $51.74   $51.75   $51.70  
  Purchase #7 $185.50   4.177%   $193.2483   $193.25   $193.25   $193.20  
  7 purchase totals = $1,213.59       $1,307.2788   $1,307.27   $1,307.25   $1,307.20