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 $249.69   10.645%   $276.2695   $276.27   $276.25   $276.30  
  Purchase #2 $200.83   10.716%   $222.3509   $222.35   $222.35   $222.40  
  Purchase #3 $39.46   9.678%   $43.2789   $43.28   $43.30   $43.30  
  Purchase #4 $76.52   3.866%   $79.4783   $79.48   $79.50   $79.50  
  Purchase #5 $17.70   9.759%   $19.4273   $19.43   $19.45   $19.40  
  Purchase #6 $195.57   5.478%   $206.2833   $206.28   $206.30   $206.30  
  Purchase #7 $105.37   8.473%   $114.298   $114.30   $114.30   $114.30  
  7 purchase totals = $885.14       $961.3862   $961.39   $961.45   $961.50