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 $183.96   5.263%   $193.6418   $193.64   $193.65   $193.60  
  Purchase #2 $15.95   13.295%   $18.0706   $18.07   $18.05   $18.10  
  Purchase #3 $112.87   10.403%   $124.6119   $124.61   $124.60   $124.60  
  Purchase #4 $133.65   9.808%   $146.7584   $146.76   $146.75   $146.80  
  Purchase #5 $84.95   5.351%   $89.4957   $89.50   $89.50   $89.50  
  Purchase #6 $187.66   11.713%   $209.6406   $209.64   $209.65   $209.60  
  Purchase #7 $200.88   8.692%   $218.3405   $218.34   $218.35   $218.30  
  7 purchase totals = $919.92       $1,000.5595   $1,000.56   $1,000.55   $1,000.50