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 $60.49   4.156%   $63.004   $63.00   $63.00   $63.00  
  Purchase #2 $117.57   7.843%   $126.791   $126.79   $126.80   $126.80  
  Purchase #3 $77.76   11.357%   $86.5912   $86.59   $86.60   $86.60  
  Purchase #4 $233.73   13.782%   $265.9427   $265.94   $265.95   $265.90  
  Purchase #5 $245.73   3.152%   $253.4754   $253.48   $253.50   $253.50  
  Purchase #6 $229.30   10.593%   $253.5897   $253.59   $253.60   $253.60  
  Purchase #7 $213.48   5.603%   $225.4413   $225.44   $225.45   $225.40  
  7 purchase totals = $1,178.06       $1,274.8353   $1,274.83   $1,274.90   $1,274.80