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 $56.46   8.509%   $61.2642   $61.26   $61.25   $61.30  
  Purchase #2 $192.26   8.294%   $208.206   $208.21   $208.20   $208.20  
  Purchase #3 $121.97   3.442%   $126.1682   $126.17   $126.15   $126.20  
  Purchase #4 $62.90   3.225%   $64.9285   $64.93   $64.95   $64.90  
  Purchase #5 $12.86   4.808%   $13.4783   $13.48   $13.50   $13.50  
  Purchase #6 $133.34   4.647%   $139.5363   $139.54   $139.55   $139.50  
  Purchase #7 $142.27   4.449%   $148.5996   $148.60   $148.60   $148.60  
  7 purchase totals = $722.06       $762.1811   $762.19   $762.20   $762.20