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 $57.90   5.471%   $61.0677   $61.07   $61.05   $61.10  
  Purchase #2 $17.26   10.630%   $19.0947   $19.09   $19.10   $19.10  
  Purchase #3 $239.83   3.512%   $248.2528   $248.25   $248.25   $248.30  
  Purchase #4 $125.57   5.853%   $132.9196   $132.92   $132.90   $132.90  
  Purchase #5 $126.60   13.748%   $144.005   $144.01   $144.00   $144.00  
  Purchase #6 $207.64   3.720%   $215.3642   $215.36   $215.35   $215.40  
  Purchase #7 $169.72   13.335%   $192.3522   $192.35   $192.35   $192.40  
  7 purchase totals = $944.52       $1,013.0562   $1,013.05   $1,013.00   $1,013.20