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 $95.91   8.287%   $103.8581   $103.86   $103.85   $103.90  
  Purchase #2 $82.75   11.515%   $92.2787   $92.28   $92.30   $92.30  
  Purchase #3 $164.83   6.531%   $175.595   $175.60   $175.60   $175.60  
  Purchase #4 $27.63   7.727%   $29.765   $29.77   $29.75   $29.80  
  Purchase #5 $125.62   8.353%   $136.113   $136.11   $136.10   $136.10  
  Purchase #6 $109.95   13.523%   $124.8185   $124.82   $124.80   $124.80  
  Purchase #7 $214.37   13.470%   $243.2456   $243.25   $243.25   $243.20  
  7 purchase totals = $821.06       $905.6739   $905.69   $905.65   $905.70