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 $11.56   13.792%   $13.1544   $13.15   $13.15   $13.20  
  Purchase #2 $198.75   8.669%   $215.9796   $215.98   $216.00   $216.00  
  Purchase #3 $142.28   9.356%   $155.5917   $155.59   $155.60   $155.60  
  Purchase #4 $176.81   8.181%   $191.2748   $191.27   $191.25   $191.30  
  Purchase #5 $80.36   8.677%   $87.3328   $87.33   $87.35   $87.30  
  Purchase #6 $63.46   10.564%   $70.1639   $70.16   $70.15   $70.20  
  Purchase #7 $198.94   8.289%   $215.4301   $215.43   $215.45   $215.40  
  7 purchase totals = $872.16       $948.9273   $948.91   $948.95   $949.00