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 $85.25   13.694%   $96.9241   $96.92   $96.90   $96.90  
  Purchase #2 $175.67   13.182%   $198.8268   $198.83   $198.85   $198.80  
  Purchase #3 $186.91   10.750%   $207.0028   $207.00   $207.00   $207.00  
  Purchase #4 $198.87   4.261%   $207.3439   $207.34   $207.35   $207.30  
  Purchase #5 $227.89   6.109%   $241.8118   $241.81   $241.80   $241.80  
  Purchase #6 $90.34   3.373%   $93.3872   $93.39   $93.40   $93.40  
  Purchase #7 $40.34   4.560%   $42.1795   $42.18   $42.20   $42.20  
  7 purchase totals = $1,005.27       $1,087.4761   $1,087.47   $1,087.50   $1,087.40