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 $33.54   3.391%   $34.6773   $34.68   $34.70   $34.70  
  Purchase #2 $178.91   3.654%   $185.4474   $185.45   $185.45   $185.40  
  Purchase #3 $103.58   10.815%   $114.7822   $114.78   $114.80   $114.80  
  Purchase #4 $223.56   5.325%   $235.4646   $235.46   $235.45   $235.50  
  Purchase #5 $197.36   10.163%   $217.4177   $217.42   $217.40   $217.40  
  Purchase #6 $160.31   3.794%   $166.3922   $166.39   $166.40   $166.40  
  Purchase #7 $221.81   13.846%   $252.5218   $252.52   $252.50   $252.50  
  7 purchase totals = $1,119.07       $1,206.7032   $1,206.70   $1,206.70   $1,206.70