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 $72.46   5.761%   $76.6344   $76.63   $76.65   $76.60  
  Purchase #2 $11.70   8.684%   $12.716   $12.72   $12.70   $12.70  
  Purchase #3 $127.26   6.615%   $135.6782   $135.68   $135.70   $135.70  
  Purchase #4 $9.70   4.420%   $10.1287   $10.13   $10.15   $10.10  
  Purchase #5 $109.61   11.762%   $122.5023   $122.50   $122.50   $122.50  
  Purchase #6 $167.47   10.286%   $184.696   $184.70   $184.70   $184.70  
  Purchase #7 $177.76   8.544%   $192.9478   $192.95   $192.95   $192.90  
  7 purchase totals = $675.96       $735.3034   $735.31   $735.35   $735.20