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 $47.62   12.577%   $53.6092   $53.61   $53.60   $53.60  
  Purchase #2 $132.36   10.512%   $146.2737   $146.27   $146.25   $146.30  
  Purchase #3 $248.89   8.716%   $270.5833   $270.58   $270.60   $270.60  
  Purchase #4 $161.35   10.422%   $178.1659   $178.17   $178.15   $178.20  
  Purchase #5 $136.54   11.646%   $152.4414   $152.44   $152.45   $152.40  
  Purchase #6 $187.53   5.778%   $198.3655   $198.37   $198.35   $198.40  
  Purchase #7 $206.80   6.590%   $220.4281   $220.43   $220.45   $220.40  
  7 purchase totals = $1,121.09       $1,219.8671   $1,219.87   $1,219.85   $1,219.90