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 $134.27   3.733%   $139.2823   $139.28   $139.30   $139.30  
  Purchase #2 $240.97   7.737%   $259.6138   $259.61   $259.60   $259.60  
  Purchase #3 $213.87   12.775%   $241.1919   $241.19   $241.20   $241.20  
  Purchase #4 $226.81   8.374%   $245.8031   $245.80   $245.80   $245.80  
  Purchase #5 $146.64   10.846%   $162.5446   $162.54   $162.55   $162.50  
  Purchase #6 $131.93   9.542%   $144.5188   $144.52   $144.50   $144.50  
  Purchase #7 $93.77   10.475%   $103.5924   $103.59   $103.60   $103.60  
  7 purchase totals = $1,188.26       $1,296.5469   $1,296.53   $1,296.55   $1,296.50