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 $60.61   12.688%   $68.3002   $68.30   $68.30   $68.30  
  Purchase #2 $99.48   12.538%   $111.9528   $111.95   $111.95   $112.00  
  Purchase #3 $104.81   10.204%   $115.5048   $115.50   $115.50   $115.50  
  Purchase #4 $114.46   5.252%   $120.4714   $120.47   $120.45   $120.50  
  Purchase #5 $20.28   11.429%   $22.5978   $22.60   $22.60   $22.60  
  Purchase #6 $244.80   3.329%   $252.9494   $252.95   $252.95   $252.90  
  Purchase #7 $76.36   7.685%   $82.2283   $82.23   $82.25   $82.20  
  7 purchase totals = $720.80       $774.0047   $774.00   $774.00   $774.00