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 $60.49   8.594%   $65.6885   $65.69   $65.70   $65.70  
  Purchase #2 $185.99   12.589%   $209.4043   $209.40   $209.40   $209.40  
  Purchase #3 $162.51   4.385%   $169.6361   $169.64   $169.65   $169.60  
  Purchase #4 $198.57   4.787%   $208.0755   $208.08   $208.10   $208.10  
  Purchase #5 $24.73   3.559%   $25.6101   $25.61   $25.60   $25.60  
  Purchase #6 $50.38   6.335%   $53.5716   $53.57   $53.55   $53.60  
  Purchase #7 $177.96   10.758%   $197.1049   $197.10   $197.10   $197.10  
  7 purchase totals = $860.63       $929.0910   $929.09   $929.10   $929.10