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 $163.77   11.171%   $182.0647   $182.06   $182.05   $182.10  
  Purchase #2 $83.44   4.448%   $87.1514   $87.15   $87.15   $87.20  
  Purchase #3 $34.25   8.741%   $37.2438   $37.24   $37.25   $37.20  
  Purchase #4 $67.84   12.813%   $76.5323   $76.53   $76.55   $76.50  
  Purchase #5 $239.64   3.503%   $248.0346   $248.03   $248.05   $248.00  
  Purchase #6 $66.31   3.865%   $68.8729   $68.87   $68.85   $68.90  
  Purchase #7 $235.62   11.226%   $262.0707   $262.07   $262.05   $262.10  
  7 purchase totals = $890.87       $961.9704   $961.95   $961.95   $962.00