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 $90.87   5.804%   $96.1441   $96.14   $96.15   $96.10  
  Purchase #2 $39.33   3.403%   $40.6684   $40.67   $40.65   $40.70  
  Purchase #3 $73.28   13.474%   $83.1537   $83.15   $83.15   $83.20  
  Purchase #4 $119.40   4.599%   $124.8912   $124.89   $124.90   $124.90  
  Purchase #5 $195.79   11.773%   $218.8404   $218.84   $218.85   $218.80  
  Purchase #6 $227.99   4.871%   $239.0954   $239.10   $239.10   $239.10  
  Purchase #7 $188.77   10.628%   $208.8325   $208.83   $208.85   $208.80  
  7 purchase totals = $935.43       $1,011.6257   $1,011.62   $1,011.65   $1,011.60