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 $190.44   8.687%   $206.9835   $206.98   $207.00   $207.00  
  Purchase #2 $136.59   13.758%   $155.3821   $155.38   $155.40   $155.40  
  Purchase #3 $59.33   4.256%   $61.8551   $61.86   $61.85   $61.90  
  Purchase #4 $242.28   11.279%   $269.6068   $269.61   $269.60   $269.60  
  Purchase #5 $212.64   10.313%   $234.5696   $234.57   $234.55   $234.60  
  Purchase #6 $8.93   10.532%   $9.8705   $9.87   $9.85   $9.90  
  Purchase #7 $67.44   13.126%   $76.2922   $76.29   $76.30   $76.30  
  7 purchase totals = $917.65       $1,014.5598   $1,014.56   $1,014.55   $1,014.70