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 $57.66   13.193%   $65.2671   $65.27   $65.25   $65.30  
  Purchase #2 $122.83   11.138%   $136.5108   $136.51   $136.50   $136.50  
  Purchase #3 $248.75   6.642%   $265.272   $265.27   $265.25   $265.30  
  Purchase #4 $231.27   13.749%   $263.0673   $263.07   $263.05   $263.10  
  Purchase #5 $155.66   10.683%   $172.2892   $172.29   $172.30   $172.30  
  Purchase #6 $109.58   3.195%   $113.0811   $113.08   $113.10   $113.10  
  Purchase #7 $204.55   12.641%   $230.4072   $230.41   $230.40   $230.40  
  7 purchase totals = $1,130.30       $1,245.8947   $1,245.90   $1,245.85   $1,246.00