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 $55.83   9.768%   $61.2835   $61.28   $61.30   $61.30  
  Purchase #2 $235.74   5.563%   $248.8542   $248.85   $248.85   $248.90  
  Purchase #3 $218.69   12.239%   $245.4555   $245.46   $245.45   $245.50  
  Purchase #4 $126.63   8.252%   $137.0795   $137.08   $137.10   $137.10  
  Purchase #5 $111.50   12.553%   $125.4966   $125.50   $125.50   $125.50  
  Purchase #6 $226.40   13.722%   $257.4666   $257.47   $257.45   $257.50  
  Purchase #7 $184.92   3.608%   $191.5919   $191.59   $191.60   $191.60  
  7 purchase totals = $1,159.71       $1,267.2278   $1,267.23   $1,267.25   $1,267.40