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 $125.58   10.319%   $138.5386   $138.54   $138.55   $138.50  
  Purchase #2 $122.98   10.863%   $136.3393   $136.34   $136.35   $136.30  
  Purchase #3 $192.98   12.522%   $217.145   $217.15   $217.15   $217.10  
  Purchase #4 $69.34   10.426%   $76.5694   $76.57   $76.55   $76.60  
  Purchase #5 $57.26   13.510%   $64.9958   $65.00   $65.00   $65.00  
  Purchase #6 $206.92   10.416%   $228.4728   $228.47   $228.45   $228.50  
  Purchase #7 $238.85   5.621%   $252.2758   $252.28   $252.30   $252.30  
  7 purchase totals = $1,013.91       $1,114.3367   $1,114.35   $1,114.35   $1,114.30