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 $86.88   9.542%   $95.1701   $95.17   $95.15   $95.20  
  Purchase #2 $22.93   8.183%   $24.8064   $24.81   $24.80   $24.80  
  Purchase #3 $103.45   6.659%   $110.3387   $110.34   $110.35   $110.30  
  Purchase #4 $85.63   12.704%   $96.5084   $96.51   $96.50   $96.50  
  Purchase #5 $205.44   8.713%   $223.34   $223.34   $223.35   $223.30  
  Purchase #6 $79.53   3.217%   $82.0885   $82.09   $82.10   $82.10  
  Purchase #7 $156.36   13.197%   $176.9948   $176.99   $177.00   $177.00  
  7 purchase totals = $740.22       $809.2469   $809.25   $809.25   $809.20