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 $84.97   12.491%   $95.5836   $95.58   $95.60   $95.60  
  Purchase #2 $187.91   7.699%   $202.3772   $202.38   $202.40   $202.40  
  Purchase #3 $163.62   13.589%   $185.8543   $185.85   $185.85   $185.90  
  Purchase #4 $89.49   5.196%   $94.1399   $94.14   $94.15   $94.10  
  Purchase #5 $94.29   8.481%   $102.2867   $102.29   $102.30   $102.30  
  Purchase #6 $27.91   4.210%   $29.085   $29.09   $29.10   $29.10  
  Purchase #7 $95.60   8.868%   $104.0778   $104.08   $104.10   $104.10  
  7 purchase totals = $743.79       $813.4045   $813.41   $813.50   $813.50