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 $231.49   13.683%   $263.1648   $263.16   $263.15   $263.20  
  Purchase #2 $71.45   6.856%   $76.3486   $76.35   $76.35   $76.30  
  Purchase #3 $217.95   3.233%   $224.9963   $225.00   $225.00   $225.00  
  Purchase #4 $77.63   12.504%   $87.3369   $87.34   $87.35   $87.30  
  Purchase #5 $43.56   4.496%   $45.5185   $45.52   $45.50   $45.50  
  Purchase #6 $114.29   8.587%   $124.1041   $124.10   $124.10   $124.10  
  Purchase #7 $237.43   9.628%   $260.2898   $260.29   $260.30   $260.30  
  7 purchase totals = $993.80       $1,081.7590   $1,081.76   $1,081.75   $1,081.70