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 $54.74   8.622%   $59.4597   $59.46   $59.45   $59.50  
  Purchase #2 $119.98   10.237%   $132.2624   $132.26   $132.25   $132.30  
  Purchase #3 $68.64   9.395%   $75.0887   $75.09   $75.10   $75.10  
  Purchase #4 $227.91   8.815%   $248.0003   $248.00   $248.00   $248.00  
  Purchase #5 $246.80   4.423%   $257.716   $257.72   $257.70   $257.70  
  Purchase #6 $22.93   3.338%   $23.6954   $23.70   $23.70   $23.70  
  Purchase #7 $6.87   7.399%   $7.3783   $7.38   $7.40   $7.40  
  7 purchase totals = $747.87       $803.6008   $803.61   $803.60   $803.70